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Definition of theory

Did you know.

The Difference Between Hypothesis and Theory

A hypothesis is an assumption, an idea that is proposed for the sake of argument so that it can be tested to see if it might be true.

In the scientific method, the hypothesis is constructed before any applicable research has been done, apart from a basic background review. You ask a question, read up on what has been studied before, and then form a hypothesis.

A hypothesis is usually tentative; it's an assumption or suggestion made strictly for the objective of being tested.

A theory , in contrast, is a principle that has been formed as an attempt to explain things that have already been substantiated by data. It is used in the names of a number of principles accepted in the scientific community, such as the Big Bang Theory . Because of the rigors of experimentation and control, it is understood to be more likely to be true than a hypothesis is.

In non-scientific use, however, hypothesis and theory are often used interchangeably to mean simply an idea, speculation, or hunch, with theory being the more common choice.

Since this casual use does away with the distinctions upheld by the scientific community, hypothesis and theory are prone to being wrongly interpreted even when they are encountered in scientific contexts—or at least, contexts that allude to scientific study without making the critical distinction that scientists employ when weighing hypotheses and theories.

The most common occurrence is when theory is interpreted—and sometimes even gleefully seized upon—to mean something having less truth value than other scientific principles. (The word law applies to principles so firmly established that they are almost never questioned, such as the law of gravity.)

This mistake is one of projection: since we use theory in general to mean something lightly speculated, then it's implied that scientists must be talking about the same level of uncertainty when they use theory to refer to their well-tested and reasoned principles.

The distinction has come to the forefront particularly on occasions when the content of science curricula in schools has been challenged—notably, when a school board in Georgia put stickers on textbooks stating that evolution was "a theory, not a fact, regarding the origin of living things." As Kenneth R. Miller, a cell biologist at Brown University, has said , a theory "doesn’t mean a hunch or a guess. A theory is a system of explanations that ties together a whole bunch of facts. It not only explains those facts, but predicts what you ought to find from other observations and experiments.”

While theories are never completely infallible, they form the basis of scientific reasoning because, as Miller said "to the best of our ability, we’ve tested them, and they’ve held up."

Two Related, Yet Distinct, Meanings of Theory

There are many shades of meaning to the word theory . Most of these are used without difficulty, and we understand, based on the context in which they are found, what the intended meaning is. For instance, when we speak of music theory we understand it to be in reference to the underlying principles of the composition of music, and not in reference to some speculation about those principles.

However, there are two senses of theory which are sometimes troublesome. These are the senses which are defined as “a plausible or scientifically acceptable general principle or body of principles offered to explain phenomena” and “an unproven assumption; conjecture.” The second of these is occasionally misapplied in cases where the former is meant, as when a particular scientific theory is derided as "just a theory," implying that it is no more than speculation or conjecture . One may certainly disagree with scientists regarding their theories, but it is an inaccurate interpretation of language to regard their use of the word as implying a tentative hypothesis; the scientific use of theory is quite different than the speculative use of the word.

  • proposition
  • supposition

hypothesis , theory , law mean a formula derived by inference from scientific data that explains a principle operating in nature.

hypothesis implies insufficient evidence to provide more than a tentative explanation.

theory implies a greater range of evidence and greater likelihood of truth.

law implies a statement of order and relation in nature that has been found to be invariable under the same conditions.

Example Sentences

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'theory.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

Late Latin theoria , from Greek theōria , from theōrein

1592, in the meaning defined at sense 6

Phrases Containing theory

  • big bang theory
  • atomic theory
  • auteur theory
  • catastrophe theory
  • cell theory
  • chaos theory
  • Bohr theory
  • decision theory
  • conspiracy theory
  • domino theory
  • critical race theory
  • devil theory
  • Galois theory
  • field theory
  • game theory
  • gauge theory
  • general theory of relativity
  • graph theory
  • group theory
  • germ theory
  • information theory
  • grand unified theory
  • kinetic theory
  • knot theory
  • number theory
  • quantity theory
  • quantum field theory
  • quantum theory
  • queer theory
  • special theory of relativity
  • steady state theory
  • string theory
  • trickle - down theory
  • undulatory theory
  • wave theory
  • theory of games
  • theory of numbers

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hypothesis

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This is the Difference Between a Hypothesis and a Theory

In scientific reasoning, they're two completely different things

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the Orthodox Church

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Cite this Entry

“Theory.” Merriam-Webster.com Dictionary , Merriam-Webster, https://www.merriam-webster.com/dictionary/theory. Accessed 3 Sep. 2023.

Kids Definition

Kids definition of theory.

from Latin theoria "a looking at or considering of facts, theory," from Greek theōria "theory, action of viewing, consideration," from theōrein "to look at, consider," — related to theater

Medical Definition

Medical definition of theory, more from merriam-webster on theory.

Nglish: Translation of theory for Spanish Speakers

Britannica English: Translation of theory for Arabic Speakers

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What Do We Mean by “Theory” in Science?

A theory is a carefully thought-out explanation for observations of the natural world that has been constructed using the scientific method, and which brings together many facts and hypotheses.

Left: Two green turtles on a log in a lake with green algae. Right: A large brown turtle with a tall shell sitting among rocks and grass.

In a previous blog post, I talked about the definition of “fact” in a scientific context , and discussed how facts differ from hypotheses and theories. The latter two terms also are well worth looking at in more detail because they are used differently by scientists and the general public, which can cause confusion when scientists talk about their work.

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With these definitions in mind, a simplified version of the scientific process would be as follows. A scientist makes an observation of a natural phenomenon. She then devises a hypothesis about the explanation of the phenomenon, and she designs an experiment and/or collects additional data to test the hypothesis. If the test falsifies the hypothesis (i.e., shows that it is incorrect), she will have to develop a new hypothesis and test that. If the hypothesis is corroborated (i.e., not falsified) by the test, the scientist will retain it. If it survives additional scrutiny, she may eventually try to incorporate it into a larger theory that helps to explain her observed phenomenon and relate it to other phenomena. 

That's all fairly abstract, so let's look at a concrete example involving some recent research I undertook with a group of collaborators. The theory of evolution states that the process of natural selection should work to optimize the function of an organism's parts if the changes increase the chances of the organism successfully producing offspring and the changes are heritable (i.e., can be passed down from generation to generation).

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But what happens when there are multiple selective pressures at work? We might hypothesize that turtles that spend most of their time in water face a trade-off between having a strong shell and one that is streamlined (making them more efficient swimmers), whereas streamlining would be less important to turtles on land, allowing them to evolve stronger shells even if they aren’t very streamlined.

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Our results corroborated our hypothesis that aquatic turtles are forced to make more of a trade-off between strength and streamlining than turtles that live on land. In general, the shell shapes of our aquatic turtles were more streamlined but weaker than those of our land turtles, and our mathematical model of natural selection indicated that selection for streamlining was acting more strongly on the aquatic species.

As with any idea in science, our results are open to further testing. For example, other researchers might develop a better model of natural selection that shows that our model was overly simplistic. Or they might collect data from more turtle species that shows that our results were based on a false pattern stemming from sampling too few species (we considered 47 species in our dataset, about 14% of living turtle species). For now, though, our results can be added as a piece of evidence that is consistent with the predictions of the large explanatory theory of evolution.

If you would like to learn more about this research, the scientific paper describing the work can be found in the Journal of Vertebrate Paleontology . You can see some of the turtle specimens that we used in this research in The Field Museum's exhibition Specimens: Unlocking the Secrets of Life , open through January 7, 2018.

kangielczyk's picture

I am a paleobiologist interested in three main topics: 1) understanding the broad implications of the paleobiology and paleoecology of extinct terrestrial vertebrates, particularly in relation to large scale problems such as the evolution of herbivory and the nature of the end-Permian mass extinction; 2) using quantitative methods to document and interpret morphological evolution in fossil and extant vertebrates; and 3) tropic network-based approaches to paleoecology. To address these problems, I integrate data from a variety of biological and geological disciplines including biostratigraphy, anatomy, phylogenetic systematics and comparative methods, functional morphology, geometric morphometrics, and paleoecology.

A list of my publications can be found here.

More information on some of my research projects and other topics can be found on the fossil non-mammalian synapsid page.

Most of my research in vertebrate paleobiology focuses on anomodont therapsids, an extinct clade of non-mammalian synapsids ("mammal-like reptiles") that was one of the most diverse and successful groups of Permian and Triassic herbivores. Much of my dissertation research concentrated on reconstructing a detailed morphology-based phylogeny for Permian members of the clade, as well as using this as a framework for studying anomodont biogeography, the evolution of the group's distinctive feeding system, and anomodont-based biostratigraphic schemes. My more recent research on the group includes: species-level taxonomy of taxa such as Dicynodon , Dicynodontoides , Diictodon , Oudenodon , and Tropidostoma ; development of a higher-level taxonomy for anomodonts; testing whether anomodonts show morphological changes consistent with the hypothesis that end-Permian terrestrial vertebrate extinctions were caused by a rapid decline in atmospheric oxygen levels; descriptions of new or poorly-known anomodonts from Antarctica, Tanzania, and South Africa; and examination of the implications of high growth rates in anomodonts. Fieldwork is an important part of my paleontological research, and recent field areas include the Parnaíba Basin of Brazil , the Karoo Basin of South Africa, the Ruhuhu Basin of Tanzania , and the Luangwa Basin of Zambia. My collaborators and I have made important discoveries in the course of these field projects, including the first remains of dinocephalian synapsids from Tanzania and a dinosaur relative that implies that the two main lineages of archosaurs (one including crocodiles and their relatives and the other including birds and dinosaurs) were diversifying in the early Middle Triassic, only a few million years after the end-Permian extinction. Finally, the experience I have gained while studying Permian and Triassic terrestrial vertebrates forms the foundation for work I am now involved in using models of food webs to investigate how different kinds of biotic and abiotic perturbations could have caused extinctions in ancient communities.

Geometric morphometrics is the basis of most of my quantitative research on evolutionary morphology, and I have been using this technique to address several biological and paleontological questions. For example, I conducted a simulation-based study of how tectonic deformation influences our ability to extract biologically-relevant shape information from fossil specimens, and the effectiveness of different retrodeformation techniques. I also used the method to address taxonomic questions in biostratigraphically-important anomodont taxa, and I served as a co-advisor for a Ph.D. student at the University of Bristol who used geometric morphometrics and finite element analysis to examine the functional significance of skull shape variation in fossil and extant crocodiles. Focusing on more biological questions, I am currently working on a large geometric morphometric study of plastron shape in extant emydine turtles. To date, I have compiled a data set of over 1600 specimens belonging to nine species, and I am using these data to address causes of variation at both the intra- and interspecific level. Some of the main goals of the work are to examine whether plastron morphology reflects a phylogeographic signal identified using molecular data in Emys marmorata , whether the "miniaturized" turtles Glyptemys muhlenbergii and Clemmys guttata have ontogenies that differ from those of their larger relatives, and how habitat preference, phylogeny, and shell kinesis affect shell morphology.

A collaborative project that began during my time as a postdoctoral researcher at the California Academy of Sciences involves using using models of trophic networks to examine how disturbances can spread through communities and cause extinctions. Our model is based on ecological principles, and some of the main data that we are using are a series of Permian and Triassic communities from the Karoo Basin of South Africa. Our research has already shown that the latest Permian Karoo community was susceptible to collapse brought on by primary producer disruption, and that the earliest Triassic Karoo community was very unstable. Presently we are investigating the mechanics that underlie this instability, and we're planning to investigate how the perturbation resistance of communities as changed over time. We've also experimented with ways to use the model to estimate the magnitude and type of disruptions needed to cause observed extinction levels during the end-Permian extinction event in the Karoo. Then there's the research project I've been working on almost my whole life .

Morphology and the stratigraphic occurrences of fossil organisms provide distinct, but complementary information about evolutionary history. Therefore, it is important to consider both sources of information when reconstructing the phylogenetic relationships of organisms with a fossil record, and I am interested how these data sources can be used together in this process. In my empirical work on anomodont phylogeny, I have consistently examined the fit of my morphology-based phylogenetic hypotheses to the fossil record because simulation studies suggest that phylogenies which fit the record well are more likely to be correct. More theoretically, I developed a character-based approach to measuring the fit of phylogenies to the fossil record. I also have shown that measurements of the fit of phylogenetic hypotheses to the fossil record can provide insight into when the direct inclusion of stratigraphic data in the tree reconstruction process results in more accurate hypotheses. Most recently, I co-advised two masters students at the University of Bristol who are examined how our ability to accurately reconstruct a clade's phylogeny changes over the course of the clade's history.

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Inside a recreated pueblo in the Crown Family PlayLab, a child and an adult play with baskets holding fake corn. Two girls stand in the doorway nearby.

What is a scientific theory?

A scientific theory is based on careful examination of facts.

scientific theory: a chalkboard being drawn on

  • The process
  • Good theory characteristics

The difference between theories, facts and laws

Additional resources, bibliography.

A scientific theory is a structured explanation to explain a group of facts or phenomena in the natural world that often incorporates a scientific hypothesis and scientific laws . The scientific definition of a theory contrasts with the definition most people use in casual language.

"The way that scientists use the word 'theory' is a little different than how it is commonly used in the lay public," said Jaime Tanner, a professor of biology at Emerson College in Boston. "Most people use the word 'theory' to mean an idea or hunch that someone has, but in science the word 'theory' refers to the way that we interpret facts."

Related: 5 sci-fi concepts that are possible (in theory)

The process of becoming a scientific theory

Every scientific theory relies on the scientific method . A scientist may make an observation and devise a hypothesis to explain that observation, then design an experiment to test that hypothesis. If the hypothesis is shown to be incorrect, the scientist will develop a new hypothesis and begin the process again. If the hypothesis is supported by the results of the experiment, it will go on to be tested again. If the hypothesis isn't disproven or surpassed by a better explanation, the scientist may incorporate it into a larger theory that helps to explain the observed phenomenon and relates it to other phenomena, according to the Field Museum . 

A scientific theory is not the end result of the scientific method; theories can be proven or rejected, just like hypotheses . And theories are continually improved or modified as more information is gathered, so that the accuracy of the prediction becomes greater over time.

Theories are foundations for furthering scientific knowledge and for putting the information gathered to practical use. Scientists use theories to develop inventions or find a cure for a disease.

Furthermore, a scientific theory is the framework for observations and facts, Tanner said. Theories may change, or the way that they are interpreted may change, but the facts themselves don't change. Tanner likens theories to a basket in which scientists keep facts and observations that they find. The shape of that basket may change as the scientists learn more and include more facts. "For example, we have ample evidence of traits in populations becoming more or less common over time (evolution), so evolution is a fact, but the overarching theories about evolution, the way that we think all of the facts go together might change as new observations of evolution are made," Tanner told Live Science.

Characteristics of a good theory

The University of California, Berkeley , defines a theory as "a broad, natural explanation for a wide range of phenomena. Theories are concise, coherent, systematic, predictive, and broadly applicable, often integrating and generalizing many hypotheses." 

According to Columbia University emeritus professor of philosophy Philip Kitcher, a good scientific theory has three characteristics. First, it has unity, which means it consists of a limited number of problem-solving strategies that can be applied to a wide range of scientific circumstances. Second, a good scientific theory leads to new questions and new areas of research. This means that a theory doesn't need to explain everything in order to be useful. And finally, a good theory is formed from a number of hypotheses that can be tested independently from the theory itself.

Any scientific theory must be based on a careful and rational examination of the facts. Facts and theories are two different things. In the scientific method, there is a clear distinction between facts, which can be observed and/or measured, and theories, which are scientists' explanations and interpretations of the facts. 

Some think that theories become laws, but theories and laws have separate and distinct roles in the scientific method. A law is a description of an observed phenomenon in the natural world that holds true every time it is tested. It doesn't explain why something is true; it just states that it is true. A theory, on the other hand, explains observations that are gathered during the scientific process. So, while law and theory are part of the scientific process, they are two different aspects, according to the National Center for Science Education . 

A good example of the difference between a theory and a law is the case of Gregor Mendel . In his research, Mendel discovered that two separate genetic traits would appear independently of each other in different offspring. "Yet, Mendel knew nothing of DNA or chromosomes . It wasn't until a century later that scientists discovered DNA and chromosomes — the biochemical explanation of Mendel's laws," said Peter Coppinger, an associate professor of biology and biomedical engineering at the Rose-Hulman Institute of Technology. "It was only then that scientists, such as T.H. Morgan working with fruit flies, explained the Law of Independent Assortment using the theory of chromosomal inheritance. Still today, this is the universally accepted explanation [theory] for Mendel's Law."

  • When does a theory become a fact? This article from Arizona State University says you're asking the wrong question! 
  • Learn the difference between the casual and scientific uses of "theory" and "law" from the cartoony stars of the Amoeba Sisters on Youtube.
  • Can a scientific theory be falsified? This article from Scientific American says no. 

Kenneth Angielczyk, "What Do We Mean by "Theory" in Science?" Field Museum, March 10, 2017. https://www.fieldmuseum.org/blog/what-do-we-mean-theory-science

University of California, Berkeley, "Science at multiple levels." https://undsci.berkeley.edu/article/0_0_0/howscienceworks_19  

Philip Kitcher, "Abusing Science: The Case Against Creationism," MIT Press, 1982. 

National Center for Science Education, "Definitions of Fact, Theory, and Law in Scientific Work," March 16, 2016 https://ncse.ngo/definitions-fact-theory-and-law-scientific-work  

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Theory Definition in Science

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The definition of a theory in science is very different from the everyday usage of the word. In fact, it's usually called a "scientific theory" to clarify the distinction. In the context of science, a theory is a well-established explanation for scientific data . Theories typically cannot be proven, but they can become established if they are tested by several different scientific investigators. A theory can be disproven by a single contrary result.

Key Takeaways: Scientific Theory

  • In science, a theory is an explanation of the natural world that has been repeatedly tested and verified using the scientific method.
  • In common usage, the word "theory" means something very different. It could refer to a speculative guess.
  • Scientific theories are testable and falsifiable. That is, it's possible a theory might be disproven.
  • Examples of theories include the theory of relativity and the theory of evolution.

There are many different examples of scientific theories in different disciplines. Examples include:

  • Physics : the big bang theory , atomic theory , theory of relativity, quantum field theory
  • Biology : the theory of evolution, cell theory, dual inheritance theory
  • Chemistry : the kinetic theory of gases, valence bond theory , Lewis theory, molecular orbital theory
  • Geology : plate tectonics theory
  • Climatology : climate change theory

Key Criteria for a Theory

There are certain criteria which must be fulfilled for a description to be a theory. A theory is not simply any description that can be used to make predictions!

A theory must do all of the following:

  • It must be well-supported by many independent pieces of evidence.
  • It must be falsifiable. In other words, it must be possible to test a theory at some point.
  • It must be consistent with existing experimental results and able to predict outcomes at least as accurately as any existing theories.

Some theories may be adapted or changed over time to better explain and predict behavior. A good theory can be used to predict natural events that have not occurred yet or have yet to be observed.

Value of Disproven Theories

Over time, some theories have been shown to be incorrect. However, not all discarded theories are useless.

For example, we now know Newtonian mechanics is incorrect under conditions approaching the speed of light and in certain frames of reference. The theory of relativity was proposed to better explain mechanics. Yet, at ordinary speeds, Newtonian mechanics accurately explains and predicts real-world behavior. Its equations are much easier to work with, so Newtonian mechanics remains in use for general physics.

In chemistry, there are many different theories of acids and bases. They involve different explanations for how acids and bases work (e.g., hydrogen ion transfer, proton transfer, electron transfer). Some theories, which are known to be incorrect under certain conditions, remain useful in predicting chemical behavior and making calculations.

Theory vs. Law

Both scientific theories and scientific laws are the result of testing hypotheses via the scientific method . Both theories and laws may be used to make predictions about natural behavior. However, theories explain why something works, while laws simply describe behavior under given conditions. Theories do not change into laws; laws do not change into theories. Both laws and theories may be falsified but contrary evidence.

Theory vs. Hypothesis

A hypothesis is a proposition which requires testing. Theories are the result of many tested hypotheses.

Theory vs Fact

While theories are well-supported and may be true, they are not the same as facts. Facts are irrefutable, while a contrary result may disprove a theory.

Theory vs. Model

Models and theories share common elements, but a theory both describes and explains while a model simply describes. Both models and theory may be used to make predictions and develop hypotheses.

  • Frigg, Roman (2006). " Scientific Representation and the Semantic View of Theories ." Theoria . 55 (2): 183–206. 
  • Halvorson, Hans (2012). "What Scientific Theories Could Not Be." Philosophy of Science . 79 (2): 183–206. doi: 10.1086/664745
  • McComas, William F. (December 30, 2013). The Language of Science Education: An Expanded Glossary of Key Terms and Concepts in Science Teaching and Learning . Springer Science & Business Media. ISBN 978-94-6209-497-0.
  • National Academy of Sciences (US) (1999). Science and Creationism: A View from the National Academy of Sciences (2nd ed.). National Academies Press. doi: 10.17226/6024 ISBN 978-0-309-06406-4. 
  • Suppe, Frederick (1998). "Understanding Scientific Theories: An Assessment of Developments, 1969–1998." Philosophy of Science . 67: S102–S115. doi: 10.1086/392812
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13.7 Cosmos & Culture

Why is 'theory' such a confusing word.

Marcelo Gleiser

A scientific theory has been tested time and time again. But the word "theory" can describe ideas that may not have any support, as well.

Theoretically speaking, there is widespread confusion about the word "theory." Right?

Many people interpret the word as iffy knowledge, based mostly on speculative thinking. It is used indiscriminately to indicate things we know — that is, based on solid empirical evidence — and things we aren't sure about. Not a good mix at all, especially when certain theories speak directly to people's religious and value-based sensitivities, such as the "theory of evolution" or "Big Bang theory." There is also the danger of falling for meaning traps set by groups with specific agendas.

Looking at the New Oxford American Dictionary (NOAD) listing for "theory" doesn't help:

  • a supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained: Darwin's theory of evolution .
  • A set of principles on which the practice of an activity is based: a theory of education .
  • An idea used to account for a situation or justify a course of action: my theory would be that...

So, there is usage within a scientific context ("the theory of...") and in a subjective context ("my theory is...") — an obvious problem.

When used in the context of a phrase, as "in theory," it gets worse. According to NOAD, "used in describing what is supposed to happen or be possible, usually with the implication that it does not in fact happen." [My italics.] Clearly, in this context, "in theory" means something that is probably wrong.

No wonder there is confusion. It is confusing!

A first step in trying to clarify the meaning(s) of theory is to understand in which context the word is being used, and to keep different contexts separate. So, if a scientist is using the word theory, as in "theory of relativity," "theory of evolution," or "Big Bang theory," it should be understood as a statement within a scientific context. In this case, a theory is certainly NOT mere subjective speculation, or something that is probably wrong, but, quite the contrary, something that has been scrutinized by the scientific process of empirical validation and has, so far, passed the test of explaining the data.

Unfortunately, even within the scientific context the word is misused, which only adds to the confusion. For example, "superstring theory" refers to a speculative theory in high-energy physics where the fundamental building blocks of matter are not elementary particles but tiny vibrating tubes of energy. Given the lack of empirical support so far for the idea, "superstring hypothesis" would be a much more appropriate characterization. Scientists may know the status of the hypothesis, but most people won't. We should be more careful.

A scientific theory is an accumulated body of knowledge constructed to describe specific natural phenomena, such as the force of gravity or biodiversity, that has been vetted by the scientific community. It is the best that we can come up with to make sense of nature at a given time.

Mind you, as our understanding of natural phenomena change, theories can change as well. This doesn't necessarily mean that the old theories are wrong . It usually means that the old theories have a limited range of validity not covered by newly discovered phenomena. For example, Newton's theory of gravity works really well to send rocket ships to Neptune, but not to describe a black hole. New theories are born from the cracks in old ones.

Unfortunately, suspicion of certain scientific theories can come from confusing subjective speculation with objective description. A scientific theory is different from a scientific hypothesis. A scientific hypothesis is an idea not yet empirically tested and, hence, still not vetted by the scientific community. A theory is a hypothesis that has been tested and vetted.

Much popular confusion could be avoided if the word theory would be understood within the right context. The often-used trap of exploring the double meaning of the word theory to confuse or willfully misguide popular opinion should only catch those who don't know, or choose to neglect, what theory means within its scientific or subjective context.

Marcelo Gleiser is a theoretical physicist and cosmologist — and professor of natural philosophy, physics and astronomy at Dartmouth College. He is the co-founder of 13.7, a prolific author of papers and essays, and active promoter of science to the general public. His latest book is The Island of Knowledge: The Limits of Science and the Search for Meaning . You can keep up with Marcelo on Facebook and Twitter: @mgleiser .

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Scientists say: theory, this is an explanation that has a lot of evidence to back it up.

what does the word theory mean in science

In 1543, Nicolaus Copernicus proposed the idea that planets go around the sun — not the sun around the planets. Almost 500 years later, his idea is now a theory — the heliocentric theory, which still applies today.

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By Bethany Brookshire

October 5, 2020 at 6:30 am

Theory (noun, “THEER-ee”)

This is an explanation about the way the natural world works. A theory explains not just what happens, but also how it happens. Theories are based on experiments, observations and facts that many scientists have confirmed, over and over. Theories also help scientists make predictions and form new questions.

Sometimes, people will say they have a theory, but they actually have a hypothesis . A hypothesis is an idea that someone can test. A theory is much more than that. It’s been tested in many ways, by many people.

A theory also organizes knowledge that applies to many different cases. For example, evolution is a theory. It states that groups of organisms change over time, and explains how that change happens: some members of a species survive to pass on their traits and others don’t. We call this a theory for two reasons. First, a huge amount of data shows that species change over time. Data from fossils show this. Data from organisms alive today show this as well. Second, these and other data explain how species change. The theory applies to all living things — animals, plants, fungi and bacteria all evolve.

Theories aren’t forever, though. If there’s new evidence that doesn’t quite fit, theories can be updated. For example, the ancient Greeks believed that diseases could spread from “seeds” of illness. Some ancient Romans also thought that tiny creatures in swamps could make people sick. In the 1800s, Louis Pasteur and Robert Koch showed that tiny organisms did cause disease — bacteria and viruses. Now, the germ theory of disease includes bacteria, fungi, viruses and more. 

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Scientists have a theory that explains how the universe began — the Big Bang theory .

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The meaning of the word theory

The normal, day-to-day meaning of the word 'theory' denotes the uncertainty regarding factuality. For instance, when we say that "it is just another theory" what we imply is that there can be many other good enough explanations and this just one of the many possible theories. But in science, the word 'theory' is used to indicate that something has successfully passed many scientific tests and it is not just another theory but it is 'the'' theory and most probably it is the truth (or at least it is a highly believable hypothesis). For instance, theory of evolution. The etymological roots of the word theory is related to the Greek word theoria [which is coming from the word theoros (meaning spectator)] and the roots of the word theory is related to the words such as speculate, contemplate, etc. The roots of the word theory match the ordinary people's day-to-day meaning of the word - not the meaning in which the word theory is used by the scientists. If so, which historical process can explain how the word theory (which lacks any guarantee of being true) got adopted to imply truthfulness in science?

  • philosophy-of-science
  • rationalism

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  • 1 I think this is a linguistics question, not a philosophy question. –  Kevin Jun 24, 2021 at 18:18
  • You are conflating the use of the word theory with its popular general population meaning as opposed to its scientific meaning. The scientific meaning of the word theory is based on the scientific method. Variations of your question have been asked and answered ad nauseam in this forum before. –  Swami Vishwananda Jun 25, 2021 at 5:19
  • A collection of sentences. –  Mauro ALLEGRANZA Jun 25, 2021 at 7:01

A 'theory' is a proposed causal explanation of an event or series of events. Technically speaking we can never 'see' causation; the best we can do is make a more (or sometimes less) informed guess about the underlying mechanism of causation. That guess is a theory.

Scientists, philosophers, scholars, intellectuals, and the like try to make theories that are robust : that seem to be functional across a range of cases and contexts. Regular people aren't quite as concerned with robustness; they are satisfied with theories that seem to make sense, or that conform to some particular narrative. Because scientists are constantly competing with each other to produce robust theories, scientific theories are generally far more functional and far more applicable than lay theories about the same subject. That intrinsic functionality gives scientific theories the countenance of truth. Even though scientific theories are not 'true' per se, they have survived active engagement with numerous attempts to tear them down, replace them, alter them, etc. Lay theories only persist because the passively or actively avoid engaging opposition.

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Theoretical Terms in Science

A simple explanation of theoreticity says that a term is theoretical if and only if it refers to nonobservational entities. Paradigmatic examples of such entities are electrons, neutrinos, gravitational forces, genes etc. There is yet another explanation of theoreticity: a theoretical term is one whose meaning becomes determined through the axioms of a scientific theory. The meaning of the term ‘force’, for example, is seen to be determined by Newton’s laws of motion and further laws about special forces, such as the law of gravitation. Theoreticity is a property that is commonly applied to both expressions in the language of science, and referents and concepts of such expressions. Objects, relations and functions as well as concepts thereof may thus qualify as theoretical in a derived sense.

Several semantics have been devised that aim to explain how a scientific theory contributes to the interpretation of its theoretical terms and as such determines what they mean and how they are understood. All of these semantics assume the respective theory to be given in an axiomatic fashion. Yet, theoretical terms are also recognizable in scientific theories which have as yet resisted a satisfying axiomatization.

Theoretical terms pertain to a number of topics in the philosophy of science. A fully fledged semantics of such terms commonly involves a statement about scientific realism and its alternatives. Such a semantics, moreover, may involve an account of how observation is related to theory in science. All formal accounts of theoretical terms deny the analytic-synthetic distinction to be applicable to the axioms of a scientific theory. The recognition of theoretical terms in the language of science by Carnap thus amounts to a rejection of an essential tenet of early logical empiricism and positivism, viz., the demonstration that all empirically significant sentences are translatable into an observation language. The present article explains the principal distinction between observational and theoretical terms, discusses important criticisms and refinements of this distinction and investigates two problems concerning the semantics of theoretical terms. Finally, the major formal accounts of this semantics are expounded.

1.1 Reference to Nonobservable Entities and Properties

1.2 semantic dependence upon a scientific theory, 2.1 criticisms, 2.2 refinements, 3.1.1 the realist view, 3.1.2 non-realist views, 3.1.3 the pythagorean view, 3.2 theoretical functions and relations, 4.1 the ramsey sentence, 4.2 indirect interpretation, 4.3 direct interpretation, 4.4 defining theoretical terms, 5. conclusion, other internet resources, related entries, 1. two criteria of theoreticity.

As just explained, a theoretical term may simply be understood as an expression that refers to nonobservable entities or properties. Theoreticity, on this understanding, is the negation of observability. This explanation of theoreticity thus rests on an antecedent understanding of observability. What makes an entity or property observable? As Carnap (1966: ch. 23) has pointed out, a philosopher understands the notion of observability in a narrower sense than a physicist. For a philosopher, a property is observable if it can be ‘directly perceived by the senses’. Hence, such properties as ‘blue’, ‘hard’ and ‘colder than’ are paradigmatic examples of observable properties in the philosopher’s understanding of observability. The physicist, by contrast, would also count quantitative magnitudes that can be measured in a ‘relatively simple, direct way’ as observable. Hence, the physicist views such quantities as temperature, pressure and intensity of electric current as observable.

The notion of direct perception is spelled out by Carnap (1966: ch. 23) by two conditions. Direct perception means, first, perception unaided by technical instruments and, second, that the perception is unaided by inferences. These two conditions are obviously not satisfied for the measurement of quantities like temperature and pressure. For the philosopher, only spatial positions of liquids and pointers are observed when these quantities are measured. To an even higher degree, we are unable to observe electrons, molecules, gravitational forces and genes on this narrow understanding of observability. Hence, expressions referring to such entities qualify as theoretical.

In sum, a property or object is observable—in the philosopher’s sense—if it can be perceived directly, where directness of observation excludes the use of technical artifacts and inferences. Notably, Carnap (1936/37: 455; 1966: 226) admits that his explanation of the distinction is not sufficiently precise to determine a sharp line between observational and theoretical terms. He rather views the theory-observation distinction as being introduced into a ‘continuum of degrees of observability’ by choice. Prominent criticisms of the theory-observation distinction will be discussed in Section 2.1 .

The above explanation of theoreticity may be felt unsatisfactory as it determines the property of being theoretical only via negation of the property of being observable (Putnam 1962). This explanation does not indicate any specific connection between the semantics of theoretical terms and corresponding scientific theories. There is, however, also a direct characterization of theoreticity that complements the criterion of non-observability: an expression is theoretical if and only if its meaning is determined through the axioms of a scientific theory. This explanation rests on what has come to be referred to as the contextual theory of meaning , which says that the meaning of a scientific term depends, in some way or other, on how this term is incorporated into a scientific theory.

Why adopt the contextual theory of meaning for scientific terms? Suppose the notion of meaning is understood along the lines of the Fregean notion of sense. The sense of a term be understood as that what determines its reference (cf. Church 1956: 6n). It is, furthermore, a reasonable requirement that a semantic theory must account for our understanding of the sense and, hence, our methods of determining the extension of scientific terms (cf. Dummett 1991: 340). For a large number of scientific terms these methods rest upon axioms of one or more scientific theories. There is no way of determining the force function in classical mechanics without using some axiom of this theory. Familiar methods make use of Newton’s second law of motion, Hooke’s law, the law of gravitation etc. Likewise, virtually all methods of measuring temperature rest upon laws of thermodynamics. Take measurement by a gas thermometer which is based on the ideal gas law. The laws of scientific theories are thus essential to our methods of determining the extension of scientific terms. The contextual theory of meaning, therefore, makes intelligible how students in a scientific discipline and scientists grasp the meaning, or sense, of scientific terms. On this account, understanding the sense of a term means knowing how to determine its referent, or extension, at least in part.

The contextual theory of meaning can be traced back at least to the work of Duhem. His demonstration that a scientific hypothesis in physics cannot be tested in isolation from its theoretical context is joined with and motivated by semantic considerations, according to which it is physical theories that give meaning to the specific concepts of physics (Duhem 1906: 183). Poincaré (1902: 90) literally claims that certain scientific propositions acquire meaning only by virtue of the adoption of certain conventions. Perhaps the most prominent and explicit formulation of the contextual theory of meaning is to be found in Feyerabend’s landmark “Explanation, Reduction, and Empiricism” (1962: 88):

For just as the meaning of a term is not an intrinsic property but is dependent upon the way in which the term has been incorporated into a theory, in the very same manner the content of a whole theory (and thereby again the meaning of the descriptive terms which it contains) depends upon the way in which it is incorporated into both the set of its empirical consequences and the set of all the alternatives which are being discussed at a given time: once the contextual theory of meaning has been adopted, there is no reason to confine its application to a single theory, especially as the boundaries of such a language or of such a theory are almost never well defined.

The accounts of a contextual theory of meaning in the works of Duhem, Poincaré and Feyerabend are informal insofar as they do not crystallize into a corresponding formal semantics for scientific terms. Such a crystallization is brought about by some of the formal accounts of theoretical terms to be expounded in Section 4 .

The view that meaning is bestowed upon a theoretical term through the axioms of a scientific theory implies that only axiomatized or axiomatizable scientific theories contain theoretical terms. In fact, all formal accounts of the semantics of theoretical terms are devised to apply to axiomatic scientific theories. This is due, in part, to the fact that physics has dominated the philosophy of science for a long time. One must wonder, therefore, whether there are any theoretical terms in, for example, evolutionary biology which has as yet resisted complete axiomatization. Arguably, there are. Even though evolutionary biology has not yet been axiomatized, we can recognize general propositions therein that are essential to determining certain concepts of this theory. Consider the following two propositions. (i) Two DNA sequences are homologous if and only if they have a common ancestor sequence. (ii) There is an inverse correlation between the number of mutations necessary to transform one DNA-sequence \(S_1\) into another \(S_2\) and the likelihood that \(S_1\) and \(S_2\) are homologous. Notably, these two propositions are used to determine, among other methods, relations of homology in evolutionary biology. The majority of general propositions in scientific theories other than those of physics, however, have instances that fail to be true. (Some philosophers of science have argued that this so even for a large number of axioms in physics [Cartwright 1983]).

2. Criticisms and Refinements of the Theory-Observation Distinction

The very idea of a clear-cut theory-observation distinction has received much criticism. First, with the help of sophisticated instruments, such as telescopes and electron microscopes, we are able to observe more and more entities, which had to be considered unobservable at a previous stage of scientific and technical evolution. Electrons and \(\alpha\)-particles which can be observed in a cloud chamber are a case in point (Achinstein 1965). Second, assume observability is understood as excluding the use of instruments. On this understanding, examples drawing on the use of cloud chambers and electron microscopes, which are adduced to criticize the theory-observation distinction, can be dealt with. However, we would then have to conclude that things being perceived with glasses are not observed either, which is counterintuitive (Maxwell 1962). Third, there are concepts applying to or being thought to apply to both macroscopic and submicroscopic particles. A case in point are spatial and temporal relations and the color concepts that play an important role in Newton’s corpuscle theory of light. Hence, there are clear-cut instances of observation concepts that apply to unobservable entities, which does not seem acceptable (cf. Putnam 1962).

These objections to the theory-observation distinction can be answered in a relatively straightforward manner from a Carnapian perspective. As explained in Section 1.1 , Carnap (1936/37, 1966) was quite explicit that the philosopher’s sense of observation excludes the use of instruments. As for an observer wearing glasses, a proponent of the theory-observation distinction finds enough material in Carnap (1936/37: 455) to defend her position. Carnap is aware of the fact that color concepts are not observable ones for a color-blind person. He is thus prepared to relativize the distinction in question. In fact, Carnap’s most explicit explanation of observability defines this notion in such a way that it is relativized to an organism (1936/37: 454n).

Recall, moreover, that Carnap’s theory-observation distinction was not intended to do justice to our overall understanding of these notions. Hence, certain quotidian and scientific uses of ‘observation’, such as observation using glasses, may well be disregarded when this distinction is drawn as long as the distinction promises to be fruitful in the logical analysis of scientific theories. A closer look reveals that Carnap (1966: 226) agrees with critics of the logical empiricists’ agenda, such as Maxwell (1962) and Achinstein (1965), on there being no clear-cut theory-observation distinction (see also Carnap’s early (1936/37: 455) for a similar statement):

There is no question here of who [the physicist thinking that temperature is observable or the philosopher who disagrees, H. A.] is using the term ‘observable’ in the right or proper way. There is a continuum which starts with direct sensory observations and proceeds to enormously complex, indirect methods of observation. Obviously no sharp line can be drawn across this continuum; it is a matter of degree.

A bit more serious is Putnam’s (1962) objection drawing on the application of apparently clear-cut instances of observation concepts to submicroscopic particles. Here, Carnap would have to distinguish between color concepts applying to observable entities and related color concepts applying to unobservable ones. So, the formal language in which the logical analysis proceeds would have to contain a predicate ‘red\(_1\)’ applying to macroscopic objects and another one ‘red\(_2\)’ applying to submicroscopic ones. Again, such a move would be in line with the artificial, or ideal language philosophy that Carnap advocated (see Lutz (2012) for a sympathetic discussion of artificial language philosophy).

There is another group of criticisms coming from the careful study of the history of science: Hanson (1958), Feyerabend (1962) and Kuhn (1962) aimed to show that observation concepts are theory-laden in a manner that makes their meaning theory-dependent. Feyerabend’s (1978: 32), for example, held that all terms are theoretical. Hanson (1958: 18) thinks that Tycho and Kepler were (literally) ‘seeing’ different things when perceiving the sun rising because their astronomical background theories were different. Kuhn (1962) was more tentative when expounding his variant of the theory-ladenness of observation. In a discussion of the Sneed formalism of the structuralist school, he favored a theory-observation distinction that is relativized, first to a theory and second to an application of this theory (Kuhn 1976).

Virtually all formal accounts of theoretical terms in fact assume that those phenomena which a theory T is meant to account for can be described in terms of expressions whose meaning does not depend on T . The counter-thesis that the meaning of putative observation terms depends on a quotidian or scientific theory, therefore, attacks a core doctrine in the logical empiricists’ and subsequent work on theoretical terms. A thorough discussion and assessment of theory-ladenness of observation in the works of the great historians of science is beyond the scope of this entry. Bird (2004), Bogen (2012) and Oberheim and Hoyningen-Huene (2009) are entries in the present encyclopedia that address, among other things, this issue. Schurz (2013: ch. 2.9) defines a criterion of the theory independence of observation in terms of an ostensive learning experiment, and shows how such a criterion helps answer the challenges of theory-ladenness of observation.

There is a simple, intuitive and influential proposal how to relativize the theory-observation distinction in a sensible way: a term t is theoretical with respect to a theory T , or for short, a T -term if and only if it is introduced by the theory T at a certain stage in the history of science. O-terms, by contrast, are those that were antecedently available and understood before T was set forth (Lewis 1970; cf. Hempel 1973). This proposal draws the theory-observation distinction in an apparently sharp way by means of relativizing that distinction to a particular theory. Needless to say, the proposal is in line with the contextual theory of meaning.

The distinction between T -terms and antecedently available O-terms has two particular merits. First, it circumvents the view that any sharp line between theoretical and observational terms is conventional and arbitrary. Second, it connects the theory-observation distinction with what seemed to have motivated that distinction in the first place, viz., an investigation how we come to understand the meaning of terms that appear to be meaningful in virtue of certain scientific theories.

A similar proposal of a relativized theory-observation distinction was made by Sneed in his seminal The Logical Structure of Mathematical Physics (1979: ch. II). Here is a simplified and more syntactic formulation of Sneed’s criterion of T -theoreticity:

Definition 1 ( T -theoreticity) A term t is theoretical with respect to the theory T , or for short, T -theoretical if and only if any method of determining the extension of t , or some part of that extension, rests on some axiom of T .

It remains to explain what it is for a method m of determining the extension of t to rest upon an axiom \(\phi\). This relation obtains if and only if the use of m depends on \(\phi\) being a true sentence. In other words, m rests upon \(\phi\) if and only if the hypothetical assumption of \(\phi\) being false or indeterminate would invalidate the use of m in the sense that we would be lacking the commonly presumed justification for using m . The qualification ‘or some part of that extension’ has been introduced in the present definition because we cannot expect a single measurement method to determine the extension of a scientific quantity completely. T -non-theoreticity is the negation of T -theoreticity:

Definition 2 ( T -non-theoreticity) A term t is T -non-theoretical if and only if it is not T -theoretical.

The concepts of classical particle mechanics (henceforth abbreviated by CPM) exemplify well the notions of T -theoreticity and T -non-theoreticity. As has been indicated above, all methods of determining the force acting upon a particle make use of some axiom of classical particle mechanics, such as Newton’s laws of motion or some law about special forces. Hence, force is CPM-theoretical. Measurement of spatial distances, by contrast, is possible without using axioms of CPM. Hence, the concept of spatial distance is CPM-non-theoretical. The concept of mass is less straightforward to classify as we can measure this concept using classical collision mechanics (CCM). Still, it was seen to be CPM-theoretical by the structuralists since CCM appeared reducible to CPM (Balzer et al. 1987: ch. 2).

Suppose for a term t once introduced by a scientific theory \(T_1\) novel methods of determination become established through another theory \(T_2\), where these methods do not depend on any axiom of \(T_1\). Then, t would neither qualify as \(T_1\)-theoretical nor as \(T_2\)-theoretical. It is preferable, in this situation, to relativize Definition 1 to theory-nets N , i.e., compounds of several theories. Whether there are such cases has not yet been settled.

The original exposition of the theoreticity criterion by Sneed (1979) is a bit more involved as it makes use of set-theoretic predicates and intended applications, rather technical notions of the structuralist approach to scientific theories . There has been a lively discussion, mainly but not exclusively within the structuralist school, how to express the relativized notion of theoreticity most properly (Balzer 1986; 1996). As noted above, Kuhn (1976) proposed a twofold relativization of theoreticity, viz., first to a scientific theory and second to applications of such theories.

Notably, Sneed’s criterion of T -theoreticity suggests a strategy that allows us to regain a global, non-relativized theory-observation distinction: simply take a term t to be theoretical if and only if it holds, for all methods m of determining its extension, that m rests upon some axiom of some theory T . A term t is non-theoretical, or observational, if and only if there are means of determining its extension, at least in part, that do not rest upon any axiom of any theory. This criterion is still relative to our present stage of explicit theories but comes closer to the original intention of Carnap’s theory-observation distinction, according to which observation is understood in the narrow sense of unaided perception.

3. Two Problems of Theoretical Terms

The problem of theoretical terms is a recurrent theme in the philosophy of science literature (Achinstein 1965; Sneed 1979: ch. II; Tuomela 1973: ch. V; Friedman 2011). Different shades of meaning have been associated with this problem. In its most comprehensive formulation, the problem of theoretical terms is to give a proper account of the meaning and reference of theoretical terms. There are at least two kinds of expression that pose a distinct problem of theoretical terms, respectively. First, unary predicates referring to theoretical entities, such as ‘electron’, ‘neutrino’ and ‘nucleotide’. Second, non-unary theoretical predicates, such as ‘homology’ in evolutionary biology and theoretical function expressions, such as ‘force’, ‘temperature’ and ‘intensity of the electromagnetic field’ in physics. Sneed’s problem of theoretical terms, as expounded in (1979: ch. II), concerns only the latter kind of expression. We shall now start surveying problems concerning the semantics of expressions for theoretical entities and then move on to expressions for theoretical relations and functions.

3.1 Theoretical Entities

A proper semantics for theoretical terms involves an account of reference and one of meaning and understanding. Reference fixing needs to be related to meaning as we want to answer the following question: how do we come to refer successfully to theoretical entities? This question calls for different answers depending on what particular conception of a theoretical entity is adopted. The issue of realism and its alternatives, therefore, comes into play at this point.

For the realist, theoretical entities exist independently of our theories about the world. Also, natural kinds that classify these entities exist independently of our theories (cf. Psillos 1999; Lewis 1984). The instrumentalist picture is commonly reported to account for theoretical entities in terms of mere fictions. The formalist variant of instrumentalism denies that theoretical terms have referents in the first place. Between these two extreme cases there is a number of intermediate positions. [ 1 ]

Carnap (1958; 1966: ch. 26) attempted to attain a metaphysically neutral position so as to avoid any commitment to or denial of scientific realism. In his account of the theoretical language of science, theoretical entities were conceived of as mathematical entities that are related to observable events in certain determinate ways. An electron, for example, figures as a certain distribution of charge and mass in a four-dimensional manifold of real numbers, where charge and mass are real-valued functions. These functions and the four-dimensional manifold itself are to be related to observable events by means of universal axioms. Notably, Carnap would not have accepted a characterization of his view as antirealist or non-realist since he thought the metaphysical doctrine of realism to be void of content.

There thus are different metaphysical views of theoretical entities in science, each of which is consistent with the understanding that a theoretical entity is inaccessible by means of unaided perception. First, theoretical entities are mind and language independent. Second, theoretical entities are mind and language dependent in some way or other. Third, they are conceived of as mathematical entities that are related to the observable world in certain determinate ways. We may thus distinguish between (i) a realist view, (ii) a collection of non-realist views and (iii) a Pythagorean view of theoretical entities.

Now, there are three major accounts of reference and meaning that have been used, implicitly or explicitly, for the semantics of theoretical terms: (i) the descriptivist picture, (ii) causal and causal-historical theories and (iii) hybrid ones that combine descriptivist ideas with causal elements (Reimer 2010). Accounts of reference and meaning other than these play no significant role in the philosophy of science. Hence, we need to survey at least nine combinations consisting, first, of an abstract characterization of the nature of a theoretical entity (realist, non-realist and Pythagorean), and, second, a particular account of reference (descriptivist, causal and hybrid). Some of these combinations are plainly inconsistent and, hence, can be dealt with very briefly. Let us start with the realist view of theoretical entities.

The descriptivist picture is highly intuitive with regard to our understanding of expressions referring to theoretical entities on the realist view. According to this picture, an electron is a spatiotemporal entity with such and such a mass and such and such a charge. We detect and recognize electrons when identifying entities having these properties. The descriptivist explanation of meaning and reference makes use of theoretical functions, mass and electric charge in the present example. The semantics of theoretical entities, therefore, is connected with the semantics of theoretical relations and functions, which will be dealt with in the next subsection. It seems to hold, in general, that theoretical entities in the sciences are to be characterized in terms of theoretical functions and relations.

The descriptivist account, however, faces two particular problems with regard to the historic evolution of scientific theories. First, if descriptions of theoretical entities are constitutive of the meaning of corresponding unary predicates, one must wonder what the common core of understanding is that adherents of successive theories share and whether there is such a core at all. Were Rutherford and Bohr talking about the same type of entities when using the expression ‘electron’? Issues of incommensurability arise with the descriptivist picture (Psillos 1999: 280). A second problem arises when elements of the description of an entity in a given theory T are judged wrong from the viewpoint of a successor theory \(T'\). Then, on a strict reading of the descriptivist account, the corresponding theoretical term failed to refer in T . For if there is nothing that satisfies a description, the corresponding expression has no referent. This is a simple consequence of the theory of description by Russell in his famous “On Denoting” (1905). Hence, an account of weighting descriptions is needed in order to circumvent such failures of reference.

As is well known, Kripke (1980) set forth a causal-historical account of reference as an alternative to the descriptivist picture. This account begins with an initial baptism that introduces a name and goes on with causal chains transmitting the reference of the name from speaker to speaker. In this picture, Aristotle is the man once baptized so; he might not have been the student of Plato or done any other thing commonly attributed to him. Kripke thought this picture to apply both to proper names and general terms. It is hardly indicated, however, how this picture works for expressions referring to theoretical entities (cf. Papineau 1996). Kripke’s story is particularly counterintuitive in view of the ahistorical manner of teaching in the natural sciences. There, up-to-date textbooks and recent journal articles are more important than the original, historical introduction of a theoretical term. The Kripkean causal story may also be read as an account of reference fixing without being read as a story of grasping the meaning of theoretical terms. Reference, however, needs to be related to meaning so as to ensure that scientists know what they are talking about and are able to identify the entities under investigation. Notably, even for expressions of everyday language, the charge of not explaining meaning has been leveled against Krikpe’s causal-historical account (Reimer 2010). The same charge applies to Putnam’s (1975) causal account of reference and meaning, which Putnam himself abandoned in his (1980).

A purely causal or causal-historical account of reference does not seem a viable option for theoretical terms. More promising are hybrid accounts that combine descriptivist intuitions with causal elements. Such an account has been given by Psillos (1999: 296):

  • A term t refers to an entity x if and only if x satisfies the core causal description associated with t .
  • Two terms \(t'\) and t denote the same entity if and only if (a) their putative referents play the same causal role with respect to a network of phenomena; and (b) the core causal description of \(t'\) takes up the kind-constitutive properties of the core causal description associated with t .

This account has two particular merits. First, it is much closer to the way scientists understand and use theoretical terms than purely causal accounts. Because of this, it is not only an account of reference but also one of meaning for theoretical terms. In purely causal accounts, by contrast, there is a tendency to abandon the notion of meaning altogether. Second, it promises to ensure a more stable notion of reference than in purely descriptivist accounts of reference and meaning. Notably, the kind of causation that Psillos’s hybrid account refers to is different from the causal-historical chains that Kripke thought responsible for the transmission of reference among speakers. No further explanation, however, is given of what a kind-constitutive property is and how we are to recognize such a property. Psillos (1999: 288n) merely infers the existence of such properties from the assumption of there being natural kinds.

Non-realist and antirealist semantics for theoretical terms are motivated by the presumption that the problem of theoretical terms has no satisfying realist solution. What does a non-realist semantics of theoretical terms look like? The view that theoretical entities are mere fictions often figures in realist portrays of antirealism. This view is hardly seriously maintained by any philosopher of science in the twentieth century. If one were to devise a formal or informal semantics for the view that theoretical entities are mere fictions, a purely descriptive account seems most promising. Such an account could in particular make heavy use of the Fregean notion of sense. For one important motivation for introducing this notion is to explain our understanding of expressions like ‘Odysseus’ and ‘Pegasus’.

Formalist variants of instrumentalism are a more serious alternative to realist semantics than the fiction view of theoretical entities. Formalist views in the philosophy of mathematics aim to account for mathematical concepts and objects in terms of syntactic entities and operations thereupon within a calculus. Such views have been carried over to theoretical concepts and objects in the natural sciences, with the qualification that the observational part of the calculus is interpreted in such a way that its symbols refer to physical or phenomenal objects. Cognitive access to theoretical entities is thus explained in terms of our cognitive access to the symbols and rules of the calculus in the context of an antecedent understanding of the observation terms. Formalist ideas were sympathetically entertained by Hermann Weyl (1949). He was driven towards such ideas by adherence to Hilbert’s distinction between real and ideal elements and the corresponding distinction between real and ideal propositions (Hilbert 1926). Propositions of the observation language were construed as real in the sense of this Hilbertian distinction, while theoretical propositions are construed as ideal. The content of an ideal proposition is understood in terms of the (syntactic) consistency of the whole system consisting of ideal and real propositions being asserted.

There remains to discuss the view that theoretical entities are mathematical entities which are related to observable events in certain determinate ways. This theory is clearly of the descriptivist type, as we shall see more clearly when dealing with the formal account by Carnap in Section 4 . No causal elements are needed in Carnap’s Pythagorean empiricism.

The Pythagorean view shifts the problem of theoretical terms to the theory of meaning and reference for mathematical expressions. The question of how we are able to refer successfully to electrons is answered by the Pythagorean by pointing out that we are able to refer successfully to mathematical entities. Moreover, the Pythagorean explains, it is part of the notion of an electron that corresponding mathematical entities are connected to observable phenomena by means of axioms and inference rules. The empirical surplus of theoretical entities in comparison to “pure” mathematical entities is thus captured by axioms and inference rules that establish connections to empirical phenomena. Since mathematical entities do not, by themselves, have connections to observable phenomena, the question of truth and falsehood may not be put in a truth-conditional manner for those axioms that connect mathematical entities with phenomenal events (cf. Section 4.2 ). Carnap (1958), therefore, came to speak of postulates when referring to the axioms of a scientific theory.

How do we come to refer successfully to mathematical entities? This, of course, is a problem in the philosophy of mathematics. (For a classical paper that addresses this problem see Benacerraf (1973)). Carnap has not much to say about meaning and reference of mathematical expressions in his seminal “The Methodological Character of Theoretical Concepts” (1956) but discusses these issues in his “Empiricism, Semantics, and Ontology” (1950). There he aims at establishing a metaphysically neutral position that avoids a commitment to Platonist, nominalist or formalist conceptions of mathematical objects. A proponent of the Pythagorean view other than Carnap is Hermann Weyl (1949). As for the cognition of mathematical entities, Weyl largely followed Hilbert’s formalism in his later work. Hence, there is a non-empty intersection between the Pythagorean view and the formalist view of theoretical entities. Unlike Carnap, Weyl did not characterize the interpretation of theoretical terms by means of model-theoretic notions.

For theoretical functions and relations, a particular problem arises from the idea that a theoretical term is, by definition, semantically dependent upon a scientific theory. Let us recall the above explanation of T -theoreticity: a term t is T -theoretical if and only if any method of determining the extension of t , or some part of that extension, rests upon some axiom of T . Let \(\phi\) be such an axiom and m be a corresponding method of determination. The present explanation of T -theoreticity, then, means that m is valid only on condition of \(\phi\) being true. The latter dependency holds because \(\phi\) is used either explicitly in calculations to determine t or in the calibration of measurement devices. Such devices, then, perform the calculation implicitly. A case in point is measurement of temperature by a gas thermometer. Such a device rests upon the law that changes of temperature result in proportional changes in the volume of gases.

Suppose now t is theoretical with respect to a theory T . Then it holds that in order to measure t , we need to assume the truth of some axiom \(\phi\) of T . Suppose, further, that t has occurrences in \(\phi\), as is standard in examples of T -theoreticity. From this it follows that, in standard truth-conditional semantics, the truth value of \(\phi\) is dependent on the semantic value of t . This leads to the following epistemological problem: on the one hand, we need to know the extension of t in order to find out whether \(\phi\) is true. On the other hand, it is simply impossible to determine the extension of t without using \(\phi\) or some other axiom of T . This mutual dependency between the semantic values of \(\phi\) and t makes it difficult, if not even impossible, to have evidence for \(\phi\) being true in any of its applications (cf. Andreas 2008).

We could, of course, use an alternative measurement method of t , say one resting upon an axiom \(\psi\) of T , to gain evidence for the axiom \(\phi\) being true in some selected instances. This move, however, only shifts the problem to applications of another axiom of T . For these applications the same type of difficulty arises, viz., mutual dependency of the semantic values of \(\psi\) and t . We are thus caught either in a vicious circle or in an infinite regress when attempting to gain evidence for the propriety of a single measurement of a theoretical term. Sneed (1979: ch. II) was the first to describe that particular difficulty in the present manner and termed it the problem of theoretical terms . Measurement of the force function in classical mechanics exemplifies this problem well. There is no method of measuring force that does not rest upon some law of classical mechanics. Likewise, it is impossible to measure temperature without using some law that depends upon either phenomenological or statistical thermodynamics.

Although its formulation is primarily epistemological, Sneed’s problem of theoretical terms has a semantic reading. Let the meaning of a term be identified with the methods of determining its extension, as suggested in Section 1.2 . Then we can say that our understanding of T -theoretical relations and functions originates from the axioms of the scientific theory T . In standard truth-conditional semantics, by contrast, one assumes that the truth value of an axiom is determined by the semantic values of those descriptive symbols which have occurrences in \(\phi\). Among these symbols, there are theoretical terms of T . Hence, it appears that standard truth-conditional semantics does not accord with the order of our grasping the meaning of theoretical terms. In the next section, we will deal with indirect means of interpreting theoretical terms. These proved to be ways out of the present problem of theoretical terms.

4. Formal Accounts

A few notational conventions and preliminary considerations are necessary to explain the formal accounts of theoretical terms. Essential to all of these accounts is the division of the set of descriptive symbols into a set \(V_o\) of observational and another set \(V_t\) of theoretical terms. (The descriptive symbols of a formal language are simply the non-logical ones.) A scientific theory thus be formulated in a language \(L(V_o,V_t)\). The division of the descriptive vocabulary gives rise to a related distinction between T - and C -axioms among the axioms of a scientific theory. The T -axioms contain only \(V_t\) symbols as descriptive ones, while the C -axioms contain both \(V_o\) and \(V_t\) symbols. The latter axioms establish a connection between the theoretical and the observational terms. TC designates the conjunction of T - and C -axioms and \(A(\TC)\) the set of these axioms. Let \(n_1 ,\ldots ,n_k\) be the elements of \(V_o\) and \(t_1 ,\ldots ,t_n\) the elements of \(V_t\). Then, TC is a proposition of the following type:

Ramsey ([1929] 1931) assumes that there is but one domain of interpretation for all descriptive symbols. Carnap (1956, 1958), by contrast, distinguishes between a domain of interpretation for observational terms and another for theoretical terms. Notably, the latter domain contains exclusively mathematical entities. Ketland (2004) has emphasized the importance of distinguishing between an observational and a theoretical domain of interpretation. TC is a first-order sentence in Ramsey’s seminal article “Theories” ([1929] 1931). Carnap (1956; 1958), however, works with higher-order logic to allow for the formulation of mathematical propositions and concepts.

where \(X_1 , \ldots ,X_n\) are higher-order variables. This sentence says that there is an extensional interpretation of the theoretical terms that verifies, together with an antecedently given interpretation of the observation language \(L(V_o)\), the axioms TC . The Ramsey sentence expresses an apparently weaker proposition than TC , at least in standard truth-conditional semantics. If one thinks that the Ramsey sentence expresses the proposition of a scientific theory more properly than TC , one holds the Ramsey view of scientific theories.

Why should one prefer the Ramsey view to the standard one? Ramsey ([1929] 1931: 231) himself seemed to have a contextual theory of meaning in mind when proposing the replacement of theoretical terms with appropriate higher-order variables:

Any additions to the theory, whether in the form of new axioms or particular assertions like \(\alpha(0, 3)\) are to be made within the scope of the original \(\alpha\), \(\beta\), \(\gamma\). They are not, therefore, strictly propositions by themselves just as the different sentences in a story beginning ‘Once upon a time’ have not complete meanings and so are not propositions by themselves.

\(\alpha\), \(\beta\), and \(\gamma\) figure in this explanation as theoretical terms to be replaced by higher-order variables. Ramsey goes on to suggest that the meaning of a theoretical sentence \(\phi\) is the difference between

  • \((\TC \wedge A \wedge \phi)^R\)
  • \((\TC \wedge A)^R\)

where A stands for the set of observation sentences being asserted and (...)\(^R\) for the operation of Ramsification, i.e., existentially generalizing on all theoretical terms. This proposal of expressing theoretical assertions clearly makes such assertions dependent upon the context of the theory TC . Ramsey ([1929] 1931: 235n) thinks that a theoretical assertion \(\phi\) is not meaningful if no observational evidence can be found for either \(\phi\) or its negation. In this case there is no stock A of observation sentences such that (1) and (2) differ in truth value.

Another important argument in favor of the Ramsey view was given later by Sneed (1979: ch. III). It is easy to show that Sneed’s problem of theoretical terms (which concerns relations and functions) does not arise in the first place on the Ramsey view. For \(\TC^R\) only says that there are extensions of the theoretical terms such that each axiom of the set \(A(\TC)\) is satisfied in the context of a given interpretation of the observational language. No claim, however, is made by \(\TC^R\) as to whether or not the sentences of \(A(\TC)\) are true. Nonetheless, it can be shown that \(\TC^R\) and TC have the same observational consequences:

Proposition 1 . For all \(L(V_o)\) sentences \(\phi\), \(\TC^R\) \(\vdash \phi\) if and only if \(\TC \vdash \phi\), where \(\vdash\) designates the relation of logical consequence in classical logic.

Hence, the Ramsey sentence cannot be true in case the original theory TC is not consistent with the observable facts. For a discussion of empirical adequacy and Ramsification see Ketland (2004).

One difficulty, however, remains with the Ramsey view. It concerns the representation of deductive reasoning, for many logicians the primary objective of logic. Now, Ramsey ([1929] 1931: 232) thinks that the ‘incompleteness’ of theoretical assertions does not affect our reasoning. No formal account, however, is given that relates our deductive practice, in which abundant use of theoretical terms is made, to the existentially quantified variables in the Ramsey sentence. We lack a translation of theoretical sentences (other than the axioms) that is in keeping with the view that the meaning of a theoretical sentence \(\phi\) is the difference between \((\TC \wedge A \wedge \phi)^R\) and \((\TC \wedge A)^R\). As Ramsey observes, it would not be correct to take \((\TC \wedge A \wedge \phi)^R\) as translation of a theoretical sentence \(\phi\) since both \((\TC \wedge A \wedge \phi)^R\) and \((\TC \wedge A \wedge \neg \phi)^R\) may well be true. Such a translation would not obey the laws of classical logic. These laws, however, are supposed to govern deductive reasoning in science. A proper semantics of theoretical terms should take the semantic peculiarities of these terms into account without revising the rules of deductive reasoning in classical logic.

There thus remains the challenge of relating the apparent use of theoretical terms in deductive scientific reasoning to the Ramsey formulation of scientific theories. Carnap was well aware of this challenge and addressed it using a sentence that became labeled later on the Carnap sentence of a scientific theory (Carnap 1958; 1966: ch. 23):

This sentence is part of a proposal to draw the analytic-synthetic distinction at the global level of a scientific theory (as this distinction proved not to be applicable to single axioms): the analytic part of the theory is given by its Carnap sentence \(A_T\), whereas the synthetic part is identified with the theory’s Ramsey sentence in light of Proposition 1. Carnap (1958) wants \(A_T\) to be understood as follows: if the Ramsey sentence is true, then the theoretical terms be interpreted such that TC comes out true as well. So, on condition of \(\TC^R\) being true, we can recover the original formulation of the theory in which the theoretical terms occur as constants. For, obviously, TC is derivable from \(\TC^R\) and \(A_T\) using Modus Ponens.

From the viewpoint of standard truth-conditional semantics, however, this instruction to interpret the Carnap sentence appears arbitrary, if not even misguided. For in standard semantics, the Ramsey sentence may well be true without TC being so (cf. Ketland 2004). Hence, the Carnap sentence would not count as analytic, as Carnap intended. Carnap’s interpretation of \(A_T\) receives a sound foundation in his (1961) proposal to define theoretical terms using Hilbert’s epsilon operator, as we shall see in Section 4.3 .

The notion of an indirect interpretation was introduced by Carnap in his Foundations of Logic and Mathematics (1939: ch. 23–24) with the intention of accounting for the semantics of theoretical terms in physics. It goes without saying that this notion is understood against the background of the notion of a direct interpretation. Carnap had the following distinction in mind. The interpretation of a descriptive symbol is direct if and only if (i) it is given by an assignment of an extension or an intension, and (ii) this assignment is made by expressions of the metalanguage. The interpretation of a descriptive symbol is indirect, by contrast, if and only if it is specified by one or several sentences of the object language, which then figure as axioms in the respective calculus. Here are two simple examples of a direct interpretation:

‘ R ’ designates the property of being rational.

‘ A ’ designates the property of being an animal.

The predicate ‘ H ’, by contrast, is interpreted in an indirect manner by a definition in the object language:

Interpretation of a symbol by a definition counts as one type of indirect interpretation. Another type is the interpretation of theoretical terms by the axioms of a scientific theory. Carnap (1939: 65) remains content with a merely syntactic explanation of indirect interpretation:

The calculus is first constructed floating in the air, so to speak; the construction begins at the top and then adds lower and lower levels. Finally, by the semantical rules, the lowest level is anchored at the solid ground of the observable facts. The laws, whether general or special, are not directly interpreted, but only the singular sentences.

The laws \(A(\TC)\) are thus simply adopted as axioms in the calculus without assuming any prior interpretation or reference to the world for theoretical terms. (A sentence \(\phi\) being an axiom of a calculus C means that \(\phi\) can be used in any formal derivation in C without being a member of the premises.) This account amounts to a formalist understanding of the theoretical language in science. It has two particular merits. First, it circumvents Sneed’s problem of theoretical terms since the axioms are not required to be true in the interpretation of the respective language that represents the facts of the theory-independent world. The need for assuming such an interpretation is simply denied. Second, the account is in line with the contextual theory meaning for theoretical terms as our understanding of such terms is explained in terms of the axioms of the respective scientific theories (cf. Section 1.2 ).

There are less formalist accounts of indirect interpretation in terms of explicit model-theoretic notions by Przelecki (1969: ch. 6) and Andreas (2010). [ 2 ] The latter account is based on ideas about theoretical terms in Carnap (1958). It emerged from an investigation into the similarities and dissimilarities between Carnapian postulates and definitions. Recall that Carnap viewed the axioms of a scientific theory as postulates since they contribute to the interpretation of theoretical terms. When explaining the Carnap sentence \(\TC^R \rightarrow \TC\), Carnap says that, if the Ramsey sentence is true, the theoretical terms are to be understood in accordance with some interpretation that satisfies TC . This is the sense in which we can say that Carnapian postulates contribute to the interpretation of theoretical terms in a manner akin to the interpretation of a defined term by the corresponding definition. Postulates and definitions alike impose a constraint on the admissible, or intended, interpretation of the complete language \(L(V)\), where V contains basic and indirectly interpreted terms.

Yet, the interpretation of theoretical terms by axioms of a scientific theory differs in several ways from that of a defined term by a definition. First, the introduction of theoretical terms may be joined with the introduction of another, theoretical domain of interpretation, in addition to the basic domain of interpretation in which observation terms are interpreted. Second, it must not be assumed that the interpretation of theoretical terms results in a unique determination of the extension of these terms. This is an implication of Carnap’s doctrine of partial interpretation (1958), as will become obvious by the end of this section. Third, axioms of a scientific theory are not conservative extensions of the observation language since they enable us to make predictions. Definitions, by contrast, must be conservative (cf. Gupta 2009). Taking these differences into account when observing the semantic similarities between definitions and Carnapian postulates suggests the following explanation: a set \(A(\TC)\) of axioms that interprets a set \(V_t\) of theoretical terms on the basis of a language \(L(V_o)\) imposes a constraint on the admissible, or intended, interpretations of the language \(L(V_o,V_t)\). An \(L(V_o,V_t)\) structure is admissible if and only if it (i) satisfies the axioms \(A(\TC)\) and (ii) extends the intended interpretation of \(L(V_o)\) to include an interpretation of the theoretical terms.

In more formal terms (Andreas 2010: 373; Przelecki 1969: ch. 6):

Definition 3 (Set \(\mathcal{S}\) of admissible structures) Let \(\mathcal{A}_o\) designate the intended interpretation of the observation language. Further, \(\MOD(A(\TC))\) designates the set of \(L(V_o,V_t)\) structures that satisfy the axioms \(A(\TC)\). \(\EXT(\mathcal{A}_o,V_t,D_t)\) is the set of \(L(V_o,V_t)\) structures that extend \(\mathcal{A}_o\) to interpret the theoretical terms, where the domain of interpretation may be extended by a domain \(D_t\) of theoretical entities.

  • \(\mathcal{S} := \MOD(A(\TC)) \cap \EXT(\mathcal{A}_o,V_t,D_t)\) if \(\MOD(A(\TC)) \cap \EXT(\mathcal{A}_o,V_t,D_t) \ne \varnothing\);
  • \(\mathcal{S} := \EXT(\mathcal{A}_o,V_t,D_t)\) if \(\MOD(A(\TC)) \cap \EXT(\mathcal{A}_o,V_t,D_t) = \varnothing\).

Given there is a range of admissible, i.e., intended structures, the following semantic rules for theoretical sentences suggest themselves:

Definition 4 (Semantics of theoretical sentences) \(\nu : L(V_o,V_t) \rightarrow \{T, F, I\}.\)

  • \(\nu(\phi) := T\) if and only if for all structures \(\mathcal{A} \in \mathcal{S}, \mathcal{A} \vDash \phi\);
  • \(\nu(\phi) := F\) if and only if for all structures \(\mathcal{A} \in \mathcal{S}, \mathcal{A} \not\vDash \phi\);
  • \(\nu(\phi) := I\) (indeterminate) if and only if there are structures \(\mathcal{A}_1, \mathcal{A}_2 \in \mathcal{S}\) such that \(\mathcal{A}_1 \vDash \phi\) but not \(\mathcal{A}_2 \vDash \phi\).

These semantic rules are motivated by supervaluation logic (van Fraassen 1969; Priest 2001: ch. 7). A sentence is true if and only if it is true in every admissible structure. It is false, by contrast, if and only if it is false in every admissible structure. And a sentence does not have a determinate truth value if and only if it is true in, at least, one admissible structure and false in, at least, another structure that is also admissible.

A few properties of the present semantics are noteworthy. First, it accounts for Carnap’s idea that the axioms \(A(\TC)\) have a twofold function, viz., setting forth empirical claims and determining the meaning of theoretical terms (Carnap 1958). For, on the one hand, the truth values of the axioms \(A(\TC)\) depend on empirical, observable facts. These axioms, on the other hand, determine the admissible interpretations of the theoretical terms. These two seemingly contradictory properties are combined by allowing the axioms \(A(\TC)\) to interpret theoretical terms only on condition of there being a structure that both extends the given interpretation of the observation language and that satisfies these axioms. If there is no such structure, the theoretical terms remain uninterpreted. This semantics, therefore, can be seen to formally work out the old contextual theory of meaning for theoretical terms.

Second, Sneed’s problem of theoretical terms ( Section 3.2 ) does not arise in the present semantics since the formulation of this problem is bound to standard truth-conditional semantics. Third, it is closely related to the Ramsey view of scientific theories as the following biconditional holds:

Proposition 2 \(\TC^R\) if and only if for all \(\phi \in A(\TC), \nu(\phi) = T\).

Unlike the Ramsey account, however, the semantics of indirect interpretation does not dispense with theoretical terms. It can rather be shown that allowing for a range of admissible interpretations as opposed to a single interpretation does not affect the validity of standard deductive reasoning (Andreas 2010). Hence, a distinctive merit of the indirect interpretation semantics of theoretical terms is that theoretical terms need not be recovered from the Ramsey sentence in the first place.

The label partial interpretation is more common in the literature to describe Carnap’s view that theoretical terms are interpreted by the axioms or postulates of a scientific theory (Suppe 1974: 86–95). The partial character of interpretation is retained in the present account since there is a range of admissible interpretations of the complete language \(L(V_o,V_t)\). This allows for the interpretation of theoretical terms to be strengthened by further postulates, just as Carnap demanded in his 1958 and 1961. To strengthen the interpretation of theoretical terms is to further constrain the range of admissible interpretations of \(L(V_o,V_t)\).

What happens if the axioms A(TC) are inconsistent or fail to be empirically adequate? In other words, what happens if there is no interpretation of the theoretical terms such that this interpretation satisfies all the axioms and agrees with the antecedent interpretation of the observation terms? In this case, the axioms of the respective theory fail to interpret the theoretical terms. The set of admissible structures, as defined by Definition 3, is empty. At the same time, we think we have some understanding of the theoretical terms, even if the respective theory fails to be fully consistent with the empirical data. For example, we think we have some understanding of the theretical terms in classical mechanics, even though classical mechanics is not universally applicable. Moreover, we seem to have inconsistent, yet non-trivial scientific theories, such as classical electrodynamics.

Consequently, Andreas (2018) generalized the present semantics so as to capture scientific reasoning in a paraconsistent setting. The proposal is based on a preferred-models semantics: satisfaction of a theory and agreement with empirical data comes in degrees. Some interpretations score better than others. This idea leads to a strict partial order of interpretations. And we understand the theoretical terms in such a manner that the set of instances of all the axioms is satisfied to a maximal extent in the context of a given interpretation of the observation terms. This proposal parallels certain adaptive logics, developed by Batens (2000) and Meheus et al. (2016). Notably, it allows us to capture scientific reasoning with ceteris paribus laws, i.e., laws that hold true most of the time but have exceptions. This could be helpful for the analysis of theoretical terms in scientific disciplines other than physics.

Relatively little research has been done on the semantics of theoretical terms in theories from scientific disciplines other than physics. It has remained an open question whether or not formal semantics that were primarily developed to capture theories in physics are applicable to theories in biology, chemistry, psychology, economics, etc. For the structuralist framework by Balzer et al. (1987) it could be shown that such applications are feasible (see Balzer et al. 2000). Rakover (2020) and McClimans (2017) studied theoretical terms in psychology, albeit without explicit considerations of their formal semantics.

Both the Ramsey view and the indirect interpretation semantics deviate from standard truth-conditional semantics at the level of theoretical terms and theoretical sentences. Such a deviation, however, was not felt to be necessary by all philosophers that have worked on theoretical concepts. Tuomela (1973: ch. V) defends a position that he calls semantic realism and that retains standard truth-conditional semantics. Hence, direct interpretation is assumed for theoretical terms by Tuomela. Yet, semantic realism for theoretical terms acknowledges there to be an epistemological distinction between observational and theoretical terms. Tuomela’s (1973: ch. I) criterion of the theory-observation distinction largely coincides with Sneed’s above expounded criterion. Since direct interpretation of theoretical terms amounts just to standard realist truth conditions, there is no need for a further discussion here.

In Weyl (1949), Carnap (1958), Feyerabend (1962) and a number of other writings, we find different formulations of the idea that the axioms of a scientific theory determine the meaning of theoretical terms without these axioms qualifying as proper definitions of theoretical terms. Lewis, however, wrote a paper with the title “How to Define Theoretical Terms” (1970). A closer look at the literature reveals that the very idea of explicitly defining theoretical terms goes back to Carnap’s (1961) use of Hilbert’s epsilon operator in scientific theories. This operator is an indefinite description operator that was introduced by Hilbert to designate some object x that satisfies an open formula \(\phi\). So

designates some x satisfying \(\phi(x)\), where x is the only free variable of \(\phi\) (cf. Avigad and Zach 2002). Now, Carnap (1961: 161n) explicitly defines theoretical terms in two steps:

where \(\bar{X}\)is a sequence of higher-order variables and \(\bar{t}\) a corresponding instantiation. So, \(\bar{t}\) designates some sequence of relations and functions that satisfies TC in the context of an antecedently given interpretation of \(V_o\). Once such a sequence has been defined via the epsilon-operator, the second step of the definition is straightforward:

Carnap showed that these definitions imply the Carnap sentence \(A_T\). Hence, they allow for direct recovery of the theoretical terms for the purpose of deductive reasoning on condition of the Ramsey sentence being true.

Lewis (1970) introduced a number of modifications concerning both the language of the Carnap sentence and its interpretation in order to attain proper definitions of theoretical terms. First, theoretical terms are considered to refer to individuals as opposed to relations and functions. This move is made coherent by allowing the basic language \(L(V_o)\) to contain relations like ‘ x has property y ’. The basic, i.e., non-theoretical language is thus no observation language in this account. Yet, it serves as the basis for introducing theoretical terms. The set \(V_o\) of ‘O-terms’ is best described as our antecedently understood vocabulary.

Second, denotationless terms are dealt with along the lines of free logic by Dana Scott (1967). An improper description, for example, denotes nothing in the domain of discourse. Atomic sentences containing denotationless terms are either true or false. An identity statement that contains a denotationless term on both sides is always true. If just one side of an identity formula has an occurrence of a denotationless term, this identity statement is false.

Third, Lewis (1970) insists on a unique interpretation of theoretical terms, thus rejecting Carnap’s doctrine of partial interpretation. Carnap (1961) is most explicit about the indeterminacy that this doctrine implies. This indeterminacy of theoretical terms drives Carnap to using Hilbert’s \(\varepsilon\)-operator there, as just explained. For Lewis, by contrast, a theoretical term is denotationless if its interpretation is not uniquely determined by the Ramsey sentence. For a scientific theory to be true, it must have a unique interpretation.

Using these modifications, Lewis transforms the Carnap sentence into three Carnap-Lewis postulates, so to speak:

These postulates look more difficult than they actually are. CL1 says that, if TC has a unique realization, then it is realized by the entities named by \(t_1,\ldots,t_k\). Realization of a theory TC , in this formulation, means interpretation of the descriptive terms under which TC comes out true, where the interpretation of the \(V_o\) terms is antecedently given. So, CL1 is to be read as saying that the theoretical terms are to be understood as designating those entities that uniquely realize TC , in the context of an antecedently given interpretation of the \(V_o\) terms. CL2 says that, if the Ramsey sentence is false, the theoretical terms do not designate anything. To see this, recall that \(\neg \exists x(x=t_i)\) means, in free logic, that \(t_i\) is denotationless. In case the theory TC has multiple realizations, the theoretical terms are denotationless too. This is expressed by CL3.

CL1–CL3 are equivalent, in free logic, to a set of sentences that properly define the theoretical terms \(t_i (1 \le i \le n)\):

\(t_i\) designates, according to this definition schema, the i -th component in that sequence of entities that uniquely realizes TC . If there is no such sequence, \(t_i (1 \le i \le n)\) is denotationless. But even if a theoretical term \(t_i\) fails to have a denotation, the definition \(D_i\) of this term remains true as long as the complete language \(L(V_o,V_t)\) is interpreted in accordance with the postulates CL1–CL3, thanks to the use of free logic.

A few further properties of Lewis’s definitions of theoretical terms are noteworthy. First, they specify the interpretation of theoretical terms uniquely. This property is obvious for the case of unique realization of TC but holds as well for the other cases since assignment of no denotation counts as interpretation of a descriptive symbol in free logic. Second, it can be shown that these definitions do not allow for the derivation of any \(L(V_o)\) sentences except logical truths, just as the original Carnap sentence did. Lewis, therefore, in fact succeeds in defining theoretical terms. He does so without attempting to divide the axioms \(A(\TC)\) into definitions and synthetic claims about the spatiotemporal world.

The replacement of theoretical relation and function symbols with individual terms was judged counterintuitive by Papineau (1996). A reformulation, however, of Lewis’s definitions using second- or higher-order variables is not difficult to accomplish, as Schurz (2005) has shown. In this reformulation the problem arises that theoretical terms are usually not uniquely interpreted since our observational evidence is most of the time insufficient to determine the extension of theoretical relation and function symbols completely. Theoretical functions, such as temperature, pressure, electromagnetic force etc., are determined only for objects that have been subjected to appropriate measurements, however indirect. In view of this problem, Schurz (2005) suggests letting the higher-order quantifiers range only over those extensions that correspond to natural kind properties. This restriction renders the requirement of unique interpretation of theoretical terms plausible once again. Such a reading was also suggested by Psillos (1999: ch. 3) with reference to Lewis’s (1984) discussion of Putnam’s (1980) model-theoretic argument. In that paper, Lewis himself suggests the restriction of the interpretation of descriptive symbols to extensions corresponding to natural kind properties.

One final note on indirect interpretation is in order. Both Carnap (1961) and Lewis (1970) interpret theoretical terms indirectly simply because any definition is an instance of an indirect interpretation. For this reason, Sneed’s problem of theoretical terms ( Section 3.2 ) does not arise. Yet, the pattern of Carnap’s and Lewis’s proposals conforms to the pattern of a definition in the narrow sense and not to the peculiar pattern of indirect interpretation that Carnap (1939) envisioned for the interpretation of theoretical terms. This is why the indirect interpretation semantics has been separated from the present discussion of defining theoretical terms.

The idea that there are scientific terms whose meaning is determined by a scientific theory goes back to Duhem and Poincaré. Such terms came to be referred to as theoretical terms in twentieth century philosophy of science. Properties and entities that are observable in the sense of direct, unaided perception did not seem to depend on scientific theories as forces, electrons and nucleotides did. Hence, philosophers of science and logicians set out to investigate the semantics of theoretical terms. Various formal accounts resulted from these investigations, among which the Ramsey sentence by Ramsey ([1929] 1931), Carnap’s notion of indirect interpretation (1939; 1958) and Lewis’s (1970) proposal of defining theoretical terms are the most prominent ones. Though not all philosophers of science understand the notion of a theoretical term in such way that semantic dependence upon a scientific theory is essential, this view prevails in the literature.

The theory-observation distinction has been attacked heavily and is presumably discredited by a large number of philosophers of science. Still, this distinction continues to permeate a number of important strands in the philosophy of science, such as scientific realism and its alternatives and the logical analysis of scientific theories. A case in point is the recent interest in the Ramsey account of scientific theories which emerged in the wake of Worral’s structural realism (cf. Ladyman 2009). We have seen, moreover, that the formal accounts of theoretical terms work well with a theory-observation distinction that is relativized to a particular theory. Critics of that distinction, by contrast, have commonly attacked a global and static division into theoretical and observational terms (Maxwell 1962; Achinstein 1965). Note finally that Carnap assigned no ontological significance to the theory-observation distinction in the sense that entities of the one type would be existent in a more genuine way than ones of the other.

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The Kid Should See This

What does the word ‘theory’ mean in science?

There’s an important difference between a scientific theory and the fanciful theories of an imaginative raconteur, and this quirk of semantics can lead to an all-too-common misconception. In general conversation, a ‘theory’ might simply mean a guess. But a scientific theory respects a somewhat stricter set of requirements. When scientists discuss theories, they are designed as comprehensive explanations for things we observe in nature. They’re founded on strong evidence and provide ways to make real-world predictions that can be tested. While scientific theories aren’t necessarily all accurate or true, they shouldn’t be belittled by their name alone. The theory of natural selection , quantum theory , the theory of general relativity and the germ theory of disease aren’t ‘just theories’. They’re structured explanations of the world around us, and the very foundation of science itself.

The Royal Institution explains what the word ‘theory’ specifically means in science in Just a Theory , animated by Jack Kenny and written by Alom Shaha.

Watch more science videos on this site, including Evidence of evolution that you can find on your body , The 12 Days of Evolution , this physical demonstration of gravitational waves , Evolutionary branching in action: Bacteria adapt to antibiotics , and Immunity and Vaccines Explained .

Bonus: The Scientific Method, animated .

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“Theory” vs. “Hypothesis”: What Is The Difference?

Chances are you’ve heard of the TV show The Big Bang Theory . Lots of people love this lighthearted sitcom for its quirky characters and their relationships, but others haven’t even given the series a chance for one reason: they don’t like science and assume the show is boring.

However, it only takes a few seconds with Sheldon and Penny to disprove this assumption and realize that this theory ab0ut The Big Bang Theory is wrong—it isn’t a scientific snoozefest.

But wait: is it a theory or a  hypothesis about the show that leads people astray? And would the actual big bang theory— the one that refers to the beginning of the universe—mean the same thing as a big bang hypothesis ?

Let’s take a closer look at theory and hypothesis to nail down what they mean.

What does theory mean?

As a noun, a theory is a group of tested general propositions “commonly regarded as correct, that can be used as principles of explanation and prediction for a class of phenomena .” This is what is known as a scientific   theory , which by definition is “an understanding that is based on already tested data or results .” Einstein’s theory of relativity and the  theory of evolution are both examples of such tested propositions .

Theory is also defined as a proposed explanation you might make about your own life and observations, and it’s one “whose status is still conjectural and subject to experimentation .” For example:  I’ve got my own theories about why he’s missing his deadlines all the time.  This example refers to an idea that has not yet been proven.

There are other uses of the word theory as well.

  • In this example,  theory is “a body of principles or theorems belonging to one subject.” It can be a branch of science or art that deals with its principles or methods .
  • For example: when she started to follow a new parenting theory based on a trendy book, it caused a conflict with her mother, who kept offering differing opinions .

First recorded in 1590–1600, theory originates from the Late Latin theōria , which stems from the Greek theōría. Synonyms for theory include approach , assumption , doctrine , ideology , method , philosophy , speculation , thesis , and understanding .

What does hypothesis mean?

Hypothesis is a noun that means “a proposition , or set of propositions, set forth as an explanation” that describe “some specified group of phenomena.” Sounds familiar to theory , no?

But, unlike a theory , a scientific  hypothesis is made before testing is done and isn’t based on results. Instead, it is the basis for further investigation . For example: her working hypothesis is that this new drug also has an unintended effect on the heart, and she is curious what the clinical trials  will show .

Hypothesis also refers to “a proposition assumed as a premise in an argument,” or “mere assumption or guess.” For example:

  • She decided to drink more water for a week to test out her hypothesis that dehydration was causing her terrible headaches.
  • After a night of her spouse’s maddening snoring, she came up with the hypothesis that sleeping on his back was exacerbating the problem.

Hypothesis was first recorded around 1590–1600 and originates from the Greek word hypóthesis (“basis, supposition”). Synonyms for hypothesis include: assumption , conclusion , conjecture , guess , inference , premise , theorem , and thesis .

How to use each

Although theory in terms of science is used to express something based on extensive research and experimentation, typically in everyday life, theory is used more casually to express an educated guess.

So in casual language,  theory and hypothesis are more likely to be used interchangeably to express an idea or speculation .

In most everyday uses, theory and hypothesis convey the same meaning. For example:

  • Her opinion is just a theory , of course. She’s just guessing.
  • Her opinion is just a hypothesis , of course. She’s just guessing.

It’s important to remember that a scientific   theory is different. It is based on tested results that support or substantiate it, whereas a hypothesis is formed before the research.

For example:

  • His  hypothesis  for the class science project is that this brand of plant food is better than the rest for helping grass grow.
  • After testing his hypothesis , he developed a new theory based on the experiment results: plant food B is actually more effective than plant food A in helping grass grow.

In these examples, theory “doesn’t mean a hunch or a guess,” according to Kenneth R. Miller, a cell biologist at Brown University. “A theory is a system of explanations that ties together a whole bunch of facts. It not only explains those facts, but predicts what you ought to find from other observations and experiments.”

So if you have a concept that is based on substantiated research, it’s a theory .

But if you’re working off of an assumption that you still need to test, it’s a hypothesis .

So remember, first comes a hypothesis , then comes theory . Now who’s ready for a  Big Bang Theory marathon?

Now that you’ve theorized and hypothesized through this whole article … keep testing your judgment (Or is it judgement?). Find out the correct spelling here!

Or find out the difference between these two common issues below!

WATCH: "Lethologica" vs. "Lethonomia": What's The Difference?

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Meaning of theory in English

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  • idea I've got an idea - why don't we ask John for help?
  • plan The plan is to hire a car when we get there.
  • thought Have you had any thoughts on presents for your mother?
  • suggestion Have you got any suggestions for improvements?
  • brainwave UK I wasn't sure what to do and then I had brainwave - I could ask Anna for help.
  • brainstorm US She was stuck until she had a brainstorm and the solution came to her.
  • It was Ptolemy who propounded the theory that the earth was at the centre of the universe .
  • This new evidence lends support to the theory that she was murdered .
  • This research seems to give some validity to the theory that the drug might cause cancer .
  • In Jungian theory, there are certain archetypes of human personality .
  • In theory, women can still have children at the age of 50.
  • aesthetically
  • anthropocentric
  • anthropocentrism
  • essentialism
  • existential
  • existentialism
  • existentialist
  • existentialistic
  • non-deterministic
  • non-philosophical
  • ontological
  • ontologically
  • spatio-temporal
  • spatiotemporally
  • superorganic
  • supersensible

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Misconceptions

In Science, It’s Never ‘Just a Theory’

what does the word theory mean in science

By Carl Zimmer

  • April 8, 2016

We asked readers to share the misconception that frustrates them the most on The New York Times — Science Facebook page. People had an array of answers, a number of which we addressed earlier this week . Judging from all the likes it quickly accumulated — far more than any other submission — this was the standout in terms of mass frustration.

Misconception: It’s just a theory.

Actually: Theories are neither hunches nor guesses. They are the crown jewels of science.

One day, it’s Megyn Kelly who has a theory about why Donald J. Trump hates her.

Another day, the newly released trailer for the next Star Wars movie inspires a million theories from fans about who Rey’s parents are.

And on Twitter , someone going by the name of Mothra P.I. has a theory about how cats can assume a new state of matter:

In everyday conversation, we tend to use the word “theory” to mean a hunch, an idle speculation, or a crackpot notion.

That’s not what “theory” means to scientists.

“In science, the word theory isn’t applied lightly,” Kenneth R. Miller, a cell biologist at Brown University, said. “It doesn’t mean a hunch or a guess. A theory is a system of explanations that ties together a whole bunch of facts. It not only explains those facts, but predicts what you ought to find from other observations and experiments.”

Dr. Miller is one of the few scientists to have explained the nature of theories on a witness stand under oath.

[ Like the Science Times page on Facebook. | Sign up for the Science Times newsletter. ]

He is a co-author of a high school biology textbook that puts a strong emphasis on the theory of evolution. In 2002, the board of education in Cobb County, Ga., adopted the textbook but also required science teachers to put a warning sticker inside the cover of every copy.

“Evolution is a theory, not a fact, regarding the origin of living things,” the sticker read, in part.

In 2004, several Cobb County parents filed a lawsuit against the county board of education to have the stickers removed. They called Dr. Miller, who testified for about two hours, explaining , among other things, the strength of evidence for the theory of evolution.

Once the lawyers had finished questioning Dr. Miller, he stepped down from the stand and made his way out of the courtroom. On the way, he noticed a woman looking him straight in the eye.

“She said, ‘It’s only a theory, and we’re going to win this one,’    ” Dr. Miller recalled.

They didn’t. In 2005 the judge ruled against the board of education. The board appealed the decision but later agreed to remove the stickers.

what does the word theory mean in science

A Week of Misconceptions

We’re using the first week of April as an opportunity to debunk some of the misconceptions about health and science that circulate all year round.

Peter Godfrey-Smith, the author of “Theory and Reality: An Introduction to the Philosophy of Science,” has been thinking about how people can avoid the misunderstanding embedded in the phrase, “It’s only a theory.”

It’s helpful, he argues, to think about theories as being like maps.

“To say something is a map is not to say it’s a hunch,” said Dr. Godfrey-Smith, a professor at the City University of New York and the University of Sydney. “It’s an attempt to represent some territory.”

A theory, likewise, represents a territory of science. Instead of rivers, hills, and towns, the pieces of the territory are facts.

“To call something a map is not to say anything about how good it is,” Dr. Godfrey-Smith added. “There are fantastically good maps where there’s not a shred of doubt about their accuracy. And there are maps that are speculative.”

To judge a map’s quality, we can see how well it guides us through its territory. In a similar way, scientists test out new theories against evidence. Just as many maps have proven to be unreliable, many theories have been cast aside.

But other theories have become the foundation of modern science, such as the theory of evolution, the general theory of relativity, the theory of plate tectonics, the theory that the sun is at the center of the solar system, and the germ theory of disease.

“To the best of our ability, we’ve tested them, and they’ve held up,” said Dr. Miller. “And that’s why we’ve held on to these things.”

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What Does Theory Mean In Science

What does the word ‘theory’ mean in science? . While scientific theories aren’t necessarily all accurate or true, they shouldn’t be belittled by their name alone. The theory of natural selection, quantum theory, the theory of general relativity and the germ theory of disease aren’t ‘just theories’. They’re structured explanations of the world around us, and the very foundation of science itself.

There’s an important difference between a scientific theory and the fanciful theories of an imaginative raconteur, and this quirk of semantics can lead to an all-too-common misconception. In general conversation, a ‘theory’ might simply mean a guess. But a scientific theory respects a somewhat stricter set of requirements. When scientists discuss theories, they are designed as comprehensive explanations for things we observe in nature. They’re founded on strong evidence and provide ways to make real-world predictions that can be tested.

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What Does Theory Mean In Science

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What Does Theory Mean In Science

What is a theory in science kid definition?

A scientific theory is an explanation for why things work or how things happen . Scientists develop theories based on their observations of the world around them. Theories are based on ideas that can be tested. Theories are not speculative, or based on a guess. ... It will explain a wide range of things.

What is theory in easy words?

A theory is a well-substantiated explanation of an aspect of the natural world that can incorporate laws, hypotheses and facts. ... A theory not only explains known facts; it also allows scientists to make predictions of what they should observe if a theory is true. Scientific theories are testable.

What is an example of a theory in science?

A scientific theory is a broad explanation that is widely accepted because it is supported by a great deal of evidence. Examples of theories in physical science include Dalton's atomic theory, Einstein's theory of gravity , and the kinetic theory of matter.

What is a scientific theory article?

A scientific theory is an explanation of an aspect of the natural world and universe that has been repeatedly tested and corroborated in accordance with the scientific method, using accepted protocols of observation, measurement, and evaluation of results.

What is the difference between a theory and law in science?

In general, a scientific law is the description of an observed phenomenon . It doesn't explain why the phenomenon exists or what causes it. The explanation for a phenomenon is called a scientific theory. It is a misconception that theories turn into laws with enough research.

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What Does Theory Mean In Science

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Scientific Theory

Table of contents, what does scientific theory mean, safeopedia explains scientific theory.

A scientific theory refers to a well established explanation of a certain aspect of the natural world, which is acquired through the use of the scientific method, and thoroughly tested and confirmed by experimentation and observation. The term "theory" in science has a different meaning from the everyday layman's use of the word, which may refer to an idea or hunch.

In technical or scientific use, the term theory fits into the same category as a principle or a law, and is considered a well established, evidence-based explanation, which accounts for currently known facts, phenomena or historically verified experience. Early in the hypothesis of the scientific method used to explain a theory, the words hypothesis and theory can be interchangeable, but as a theory is supported by more evidence and support data, it may still maintain the label of theory even after it has evolved from mere conjecture to established fact.

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  1. Theory Definition & Meaning

    theory noun the· o· ry ˈthē-ə-rē ˈthir-ē plural theories Synonyms of theory 1 : a plausible or scientifically acceptable general principle or body of principles offered to explain phenomena the wave theory of light 2 a : a belief, policy, or procedure proposed or followed as the basis of action

  2. What Is a Theory? A Scientific Definition

    A theory is a well-substantiated explanation of an aspect of the natural world that can incorporate laws, hypotheses and facts. The theory of gravitation, for instance, explains why apples fall from trees and astronauts float in space.

  3. What Do We Mean by "Theory" in Science?

    A theory is a carefully thought-out explanation for observations of the natural world that has been constructed using the scientific method, and which brings together many facts and hypotheses. In a previous blog post, I talked about the definition of "fact" in a scientific context, and discussed how facts differ from hypotheses and theories.

  4. What is a scientific theory?

    A scientific theory is a structured explanation to explain a group of facts or phenomena in the natural world that often incorporates a scientific hypothesis and scientific laws. The scientific...

  5. Theory Definition & Meaning

    a particular conception or view of something to be done or of the method of doing it; a system of rules or principles: conflicting theories of how children best learn to read. contemplation or speculation: the theory that there is life on other planets. guess or conjecture: My theory is that he never stops to think words have consequences.

  6. Theory Definition in Science

    In science, a theory is an explanation of the natural world that has been repeatedly tested and verified using the scientific method. In common usage, the word "theory" means something very different. It could refer to a speculative guess. Scientific theories are testable and falsifiable. That is, it's possible a theory might be disproven.

  7. Why Is 'Theory' Such A Confusing Word?

    a supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained: Darwin's theory of evolution. A set of...

  8. Scientists Say: Theory

    Theory (noun, "THEER-ee") This is an explanation about the way the natural world works. A theory explains not just what happens, but also how it happens. Theories are based on experiments, observations and facts that many scientists have confirmed, over and over. Theories also help scientists make predictions and form new questions.

  9. Scientific theory Definition & Meaning

    noun a coherent group of propositions formulated to explain a group of facts or phenomena in the natural world and repeatedly confirmed through experiment or observation: the scientific theory of evolution. What's So Wrong With "Nice"? What's So Wrong With "Nice"? NOW PLAYING British Slang: Take The Quiz! I.E. Vs E.G.

  10. Scientific theory

    A scientific theory is an explanation of an aspect of the natural world and universe that can be (or a fortiori, that has been) repeatedly tested and corroborated in accordance with the scientific method, using accepted protocols of observation, measurement, and evaluation of results. Where possible, theories are tested under controlled ...

  11. "Just a Theory": 7 Misused Science Words

    1. Hypothesis The general public so widely misuses the words hypothesis, theory and law that scientists should stop using these terms, writes physicist Rhett Allain of Southeastern Louisiana...

  12. The meaning of the word theory

    1. A 'theory' is a proposed causal explanation of an event or series of events. Technically speaking we can never 'see' causation; the best we can do is make a more (or sometimes less) informed guess about the underlying mechanism of causation. That guess is a theory. Scientists, philosophers, scholars, intellectuals, and the like try to make ...

  13. Theoretical Terms in Science

    Theoretical terms pertain to a number of topics in the philosophy of science. A fully fledged semantics of such terms commonly involves a statement about scientific realism and its alternatives. Such a semantics, moreover, may involve an account of how observation is related to theory in science.

  14. What does the word 'theory' mean in science?

    In general conversation, a 'theory' might simply mean a guess. But a scientific theory respects a somewhat stricter set of requirements. When scientists discuss theories, they are designed as comprehensive explanations for things we observe in nature.

  15. "Theory" vs. "Hypothesis": What Is The Difference?

    What does theory mean? As a noun, a theory is a group of tested general propositions "commonly regarded as correct, that can be used as principles of explanation and prediction for a class of phenomena." This is what is known as a scientific theory, which by definition is "an understanding that is based on already tested data or results."

  16. 1.3: Scientific Theories

    Scientific Theories. With repeated testing, some hypotheses may eventually become scientific theories. Keep in mind, a hypothesis is a possible answer to a scientific question. A scientific theory is a broad explanation for events that is widely accepted as true. To become a theory, a hypothesis must be tested over and over again, and it must be supported by a great deal of evidence.

  17. THEORY

    theory definition: 1. a formal statement of the rules on which a subject of study is based or of ideas that are…. Learn more.

  18. In Science, It's Never 'Just a Theory'

    That's not what "theory" means to scientists. "In science, the word theory isn't applied lightly," Kenneth R. Miller, a cell biologist at Brown University, said. "It doesn't mean a ...

  19. How is the use of the word theory in science different from

    Put the scrambled letters in order to spell a science term: A metric unit of time _____ (dceson) biology. Fill in the blanks with the term that best completes the sentence. Science uses____ to support its explanations. economics. Your boss decides to pair workers in teams and offer bonuses to the most productive team.

  20. What Does Theory Mean In Science

    What Does Theory Mean In Science | Science-Atlas.com What does the word 'theory' mean in science? . While scientific theories aren't necessarily all accurate or true, they shouldn't be belittled by their... Scientific discoveries from around the world News Astronomy Technology Space Planet Earth Animals Biology Chemistry Culture Earth Health

  21. Scientific Theory

    A scientific theory refers to a well established explanation of a certain aspect of the natural world, which is acquired through the use of the scientific method, and thoroughly tested and confirmed by experimentation and observation. The term "theory" in science has a different meaning from the everyday layman's use of the word, which may ...

  22. What do scientists mean when they use the word 'theory'? You often hear

    A scientific theory by definition cannot be proved beyond doubt, for if it is, it then moves into the realm of scientific fact. Scientific theories, however, are far more than unsubstantiated ...

  23. What does the word "theory" mean in science?

    Colloquially theory is used to mean "a guess" but in science it means a framework that best explains all available data and allows for novel predictions and future hypotheses. What the cern scientist might have been saying is that theories generally aren't the type of thing that can be directly tested. You can't test "the germ theory."