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A theory is a
rational Rationality is the quality or state of being rational – that is, being based on or agreeable to reason Reason is the capacity of consciously making sense of things, applying logic Logic (from Ancient Greek, Greek: grc, wikt:λογι ...
type of
abstract
abstract
thinking about a
phenomenon A phenomenon (; plural phenomena) is an observable In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies mat ...
, or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes as
observational study In fields such as epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants In mathematics, the determinant is a Scalar (mathematics), scalar value that is a function (mathematics), ...
or
research Research is "creative and systematic work undertaken to increase the stock of knowledge". It involves the collection, organization and analysis of information to increase understanding of a topic or issue. A research project may be an expa ...

research
. Theories may be
scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. The usual test for a statement of fac ...
, belong to a non-scientific discipline, or no discipline at all. Depending on the context, a theory's assertions might, for example, include generalized explanations of how
nature Nature, in the broadest sense, is the natural, physical, material world or universe The universe ( la, universus) is all of space and time and their contents, including planets, stars, galaxy, galaxies, and all other forms of matter an ...
works. The word has its roots in
ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the diale ...
, but in modern use it has taken on several related meanings. In modern
science Science () is a systematic enterprise that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe."... modern science is a discovery as well as an invention. ...

science
, the term "theory" refers to
scientific theories A scientific theory is an explanation of an aspect of the natural science, natural world and universe that can be reproducibility, repeatedly tested and verified in accordance with the scientific method, using accepted protocol (science), protocol ...
, a well-confirmed type of explanation of
nature Nature, in the broadest sense, is the natural, physical, material world or universe The universe ( la, universus) is all of space and time and their contents, including planets, stars, galaxy, galaxies, and all other forms of matter an ...

nature
, made in a way
consistent In classical deductive logic Deductive reasoning, also deductive logic, is the process of reasoning from one or more statements (premises) to reach a logical conclusion. Deductive reasoning goes in the same direction as that of the conditiona ...

consistent
with the
scientific method The scientific method is an empirical Empirical evidence for a proposition is evidence, i.e. what supports or counters this proposition, that is constituted by or accessible to sense experience or experimental procedure. Empirical evidence ...

scientific method
, and fulfilling the
criteria Criterion, or its plural form criteria, may refer to: General * Criterion, Oregon, a historic unincorporated community in the United States * Criterion Place, a proposed skyscraper in West Yorkshire, England * Criterion Restaurant, in London, Engl ...
required by
modern science The history of science covers the development of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of ...
. Such theories are described in such a way that scientific tests should be able to provide
empirical Empirical evidence for a proposition is evidence, i.e. what supports or counters this proposition, that is constituted by or accessible to sense experience or experimental procedure. Empirical evidence is of central importance to the sciences and ...
support for it, or empirical contradiction ("
falsify In the philosophy of science, a theory is falsifiable if it is contradicted by ''possible observations''—i.e., by any observations that can be described in the language of the theory, which must have a wiktionary:conventional, conventional Evi ...
") of it. Scientific theories are the most reliable, rigorous, and comprehensive form of scientific knowledge, in contrast to more common uses of the word "theory" that imply that something is unproven or speculative (which in formal terms is better characterized by the word ''
hypothesis A hypothesis (plural hypotheses) is a proposed explanation An explanation is a set of statements usually constructed to describe a set of facts which clarifies the causes, context Context may refer to: * Context (language use), the rel ...
''). Scientific theories are distinguished from hypotheses, which are individual empirically
testable Testability, a property applying to an empirical hypothesis, involves two components: #Falsifiability or defeasibility, which means that counterexamples to the hypothesis are logically possible. #The practical feasibility of observing a reproducibi ...
conjecture In mathematics Mathematics (from Greek: ) includes the study of such topics as numbers ( and ), formulas and related structures (), shapes and spaces in which they are contained (), and quantities and their changes ( and ). There is no ge ...
s, and from
scientific laws Scientific laws or laws of science are statements, based on repeated experiment An experiment is a procedure carried out to support, refute, or validate a hypothesis. Experiments provide insight into Causality, cause-and-effect by demonstrat ...
, which are descriptive accounts of the way nature behaves under certain conditions. Theories guide the enterprise of finding facts rather than of reaching goals, and are neutral concerning alternatives among values. A theory can be a
body of knowledge A body of knowledge (BOK or BoK) is the complete set of concepts, terms and activities that make up a professional A professional is a member of a profession or any person who earns a living from a specified professional activity. The term also d ...
, which may or may not be associated with particular explanatory
models
models
. To theorize is to develop this body of knowledge. The word theory or "in theory" is sometimes used erroneously by people to explain something which they individually did not experience or test before. In those instances, semantically, it is being substituted for another
concept Concepts are defined as abstract ideas A mental representation (or cognitive representation), in philosophy of mind Philosophy of mind is a branch of philosophy that studies the ontology and nature of the mind and its relationship with the bod ...

concept
, a
hypothesis A hypothesis (plural hypotheses) is a proposed explanation An explanation is a set of statements usually constructed to describe a set of facts which clarifies the causes, context Context may refer to: * Context (language use), the rel ...
. Instead of using the word "hypothetically", it is replaced by a phrase: "in theory". In some instances the theory's credibility could be contested by calling it "just a theory" (implying that the idea has not even been tested). Hence, that word "theory" is very often contrasted to " practice" (from Greek ''
praxis Praxis may refer to: Philosophy and religion *Praxis (process), the process by which a theory, lesson, or skill is enacted, practiced, embodied, or realized *Praxis model, a way of doing theology * Praxis (Byzantine Rite), the practice of faith, ...
'', πρᾶξις) a Greek term for ''doing'', which is opposed to theory.David J Pfeiffer.
Scientific Theory vs Law
'.
Science Journal ''New Scientist'', first published on 22 November 1956, is a magazine that covers all aspects of science and technology. Based in London, it publishes weekly English-language editions in the UK, the United States, and Australia. An editorially se ...
(on medium.com). 30 January 2017
A "classical example" of the distinction between "theoretical" and "practical" uses the discipline of medicine:
medical theory Medical research (or biomedical research), also known as experimental medicine, encompasses a wide array of research, extending from "basic research Basic research, also called pure research or fundamental research, is a type of scientific r ...
involves trying to understand the
causesCauses, or causality, is the relationship between one event and another. It may also refer to: * Causes (band), an indie band based in the Netherlands * Causes (company), an online company See also

* Cause (disambiguation) {{disambiguation ...
and nature of health and sickness, while the practical side of medicine is trying to make people healthy. These two things are related but can be independent, because it is possible to research health and sickness without curing specific patients, and it is possible to cure a patient without knowing how the cure worked.


Ancient usage

The English word ''theory'' derives from a technical term in
philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about Metaphysics, existence, reason, Epistemology, knowledge, Ethics, values, Philosophy of mind, mind, and Philosophy of language, language. Such questio ...

philosophy
in
Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the diale ...
. As an everyday word, ''
theoria Christian contemplation, from ''contemplatio'' (Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as ...
'', , meant "looking at, viewing, beholding", but in more technical contexts it came to refer to
contemplative Nature contemplation Whilst in the life of the intellect 'contemplation' refers to thinking profoundly about something, in the religious life contemplation is a kind of inner vision or seeing, transcendent of the intellect, facilitated by mean ...

contemplative
or speculative understandings of natural things, such as those of natural philosophers, as opposed to more practical ways of knowing things, like that of skilled orators or artisans. English-speakers have used the word ''theory'' since at least the late
16th century The 16th century begins with the Julian calendar, Julian year 1501 (Roman numerals, MDI) and ends with either the Julian or the Gregorian calendar, Gregorian year 1600 (Roman numerals, MDC) (depending on the reckoning used; the Gregorian calend ...
. Modern uses of the word ''theory'' derive from the original definition, but have taken on new shades of meaning, still based on the idea of a theory as a thoughtful and
rational Rationality is the quality or state of being rational – that is, being based on or agreeable to reason Reason is the capacity of consciously making sense of things, applying logic Logic (from Ancient Greek, Greek: grc, wikt:λογι ...
explanation of the general
nature Nature, in the broadest sense, is the natural, physical, material world or universe The universe ( la, universus) is all of space and time and their contents, including planets, stars, galaxy, galaxies, and all other forms of matter an ...
of things. Although it has more mundane meanings in Greek, the word apparently developed special uses early in the recorded history of the
Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the dialects of the Greek language spoken in the modern era, including the ...
. In the book ''From Religion to Philosophy'',
Francis Cornford Francis Macdonald Cornford (27 February 1874 – 3 January 1943) was an English classical scholar Classics or classical studies is the study of classical antiquity, and in the Western world The Western world, also known as the W ...
suggests that the
Orphics Orphism (more rarely Orphicism; grc, Ὀρφικά, Orphiká) is the name given to a set of religious beliefs and practices originating in the ancient Greek and Hellenistic world, as well as from the Thracians, associated with literature ascribed t ...
used the word ''theoria'' to mean "passionate sympathetic contemplation".
Pythagoras Pythagoras of Samos, or simply ; in Ionian Greek () was an ancient Ionians, Ionian Ancient Greek philosophy, Greek philosopher and the eponymous founder of Pythagoreanism. His political and religious teachings were well known in Magna Graec ...

Pythagoras
changed the word to mean "the passionless contemplation of rational, unchanging truth" of mathematical knowledge, because he considered this intellectual pursuit the way to reach the highest plane of existence. Pythagoras emphasized subduing emotions and bodily desires to help the intellect function at the higher plane of theory. Thus, it was Pythagoras who gave the word ''theory'' the specific meaning that led to the classical and modern concept of a distinction between theory (as uninvolved, neutral thinking) and practice. Aristotle's terminology, as already mentioned, contrasts theory with ''praxis'' or practice, and this contrast exists till today. For Aristotle, both practice and theory involve thinking, but the aims are different. Theoretical contemplation considers things humans do not move or change, such as
nature Nature, in the broadest sense, is the natural, physical, material world or universe The universe ( la, universus) is all of space and time and their contents, including planets, stars, galaxy, galaxies, and all other forms of matter an ...
, so it has no human aim apart from itself and the knowledge it helps create. On the other hand, ''praxis'' involves thinking, but always with an aim to desired actions, whereby humans cause change or movement themselves for their own ends. Any human movement that involves no conscious choice and thinking could not be an example of ''praxis'' or doing.


Formality

Theories are tools for
understanding Understanding is a psychological process related to an abstract or physical thing, such as a person, situation, or message whereby one is able to use concepts to model that thing. Understanding is a relation between the knower and an object of u ...

understanding
, explaining, and making
prediction Image:Old Farmer's Almanac 1793 cover.jpg, frame, ''The Old Farmer's Almanac'' is famous in the US for its (not necessarily accurate) long-range weather predictions. A prediction (Latin ''præ-'', "before," and ''dicere'', "to say"), or forecas ...
s about a given subject matter. There are theories in many and varied fields of study, including the
art Art is a diverse range of (products of) human activities Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intelligence allowing the use ...

art
s and
science Science () is a systematic enterprise that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe."... modern science is a discovery as well as an invention. ...

science
s. A formal theory is
syntactic In linguistics Linguistics is the scientific study of language, meaning that it is a comprehensive, systematic, objective, and precise study of language. Linguistics encompasses the analysis of every aspect of language, as well as the ...
in nature and is only meaningful when given a
semantic Semantics (from grc, σημαντικός ''sēmantikós'', "significant") is the study of reference Reference is a relationship between objects in which one object designates, or acts as a means by which to connect to or link to, another ...
component by applying it to some content (e.g.,
fact A fact is something that is true True most commonly refers to truth Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In everyday language, truth is typically ascribed to things ...
s and relationships of the actual historical world as it is unfolding). Theories in various fields of study are expressed in
natural language In neuropsychology Neuropsychology is a branch of psychology. It is concerned with how a person's cognition and behavior are related to the brain and the rest of the nervous system. Professionals in this branch of psychology often focus on ...
, but are always constructed in such a way that their general form is identical to a theory as it is expressed in the
formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbol (formal), letters are taken from an alphabet (computer science), alphabet and are well-formedness, well-formed a ...
of
mathematical logic Mathematical logic is the study of formal logic within mathematics. Major subareas include model theory, proof theory, set theory, and recursion theory. Research in mathematical logic commonly addresses the mathematical properties of formal sys ...
. Theories may be expressed mathematically, symbolically, or in common language, but are generally expected to follow principles of
rational thought Rationality is the quality or state of being rational – that is, being based on or agreeable to reason. Rationality implies the conformity of one's beliefs with one's reason (argument), reasons to believe, and of one's actions with one's reas ...
or
logic Logic is an interdisciplinary field which studies truth and reasoning. Informal logic seeks to characterize Validity (logic), valid arguments informally, for instance by listing varieties of fallacies. Formal logic represents statements and ar ...

logic
. Theory is constructed of a set of
sentences ''The Four Books of Sentences'' (''Libri Quattuor Sententiarum'') is a book of theology Theology is the systematic study of the nature of the Divinity, divine and, more broadly, of religious belief. It is taught as an Discipline (academia), aca ...
that are entirely true statements about the subject under consideration. However, the truth of any one of these statements is always relative to the whole theory. Therefore, the same statement may be true with respect to one theory, and not true with respect to another. This is, in ordinary language, where statements such as "He is a terrible person" cannot be judged as true or false without reference to some
interpretation Interpretation may refer to: Culture * Aesthetic interpretation, an explanation of the meaning of a work of art * Allegorical interpretation, an approach that assumes a text should not be interpreted literally * Dramatic Interpretation, an event i ...
of who "He" is and for that matter what a "terrible person" is under the theory.Curry, Haskell, ''Foundations of Mathematical Logic'' Sometimes two theories have exactly the same
explanatory power Explanatory power is the ability of a hypothesis or theory A theory is a reason, rational type of abstraction, abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often ass ...
because they make the same predictions. A pair of such theories is called indistinguishable or observationally equivalent, and the choice between them reduces to convenience or philosophical preference. The form of theories is studied formally in mathematical logic, especially in
model theory In mathematical logic Mathematical logic is the study of formal logic within mathematics. Major subareas include model theory, proof theory, set theory, and recursion theory. Research in mathematical logic commonly addresses the mathematical p ...
. When theories are studied in mathematics, they are usually expressed in some formal language and their statements are closed under application of certain procedures called
rules of inference In the philosophy of logic, a rule of inference, inference rule or transformation rule is a logical form consisting of a function which takes premises, analyzes their Syntax (logic), syntax, and returns a conclusion (or multiple-conclusion logic, ...
. A special case of this, an axiomatic theory, consists of
axioms An axiom, postulate or assumption is a statement that is taken to be truth, true, to serve as a premise or starting point for further reasoning and arguments. The word comes from the Greek ''axíōma'' () 'that which is thought worthy or fit' or ...
(or axiom schemata) and rules of inference. A
theorem In mathematics, a theorem is a statement (logic), statement that has been Mathematical proof, proved, or can be proved. The ''proof'' of a theorem is a logical argument that uses the inference rules of a deductive system to establish that the the ...
is a statement that can be derived from those axioms by application of these rules of inference. Theories used in applications are
abstraction Abstraction in its main sense is a conceptual process where general rules Rule or ruling may refer to: Human activity * The exercise of political Politics (from , ) is the set of activities that are associated with Decision-making, mak ...

abstraction
s of observed phenomena and the resulting theorems provide solutions to real-world problems. Obvious examples include
arithmetic Arithmetic (from the Ancient Greek, Greek wikt:en:ἀριθμός#Ancient Greek, ἀριθμός ''arithmos'', 'number' and wikt:en:τική#Ancient Greek, τική wikt:en:τέχνη#Ancient Greek, έχνη ''tiké échne', 'art' or 'cr ...
(abstracting concepts of number),
geometry Geometry (from the grc, γεωμετρία; ' "earth", ' "measurement") is, with , one of the oldest branches of . It is concerned with properties of space that are related with distance, shape, size, and relative position of figures. A mat ...

geometry
(concepts of space), and
probability Probability is the branch of mathematics Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces in which they are contained ...

probability
(concepts of randomness and likelihood). Gödel's incompleteness theorem shows that no consistent,
recursively enumerable In computability theory, traditionally called recursion theory, a set ''S'' of natural numbers is called recursively enumerable, computably enumerable, semidecidable, partially decidable, listable, provable or Turing-recognizable if: *There is a ...
theory (that is, one whose theorems form a recursively enumerable set) in which the concept of
natural numbers In mathematics, the natural numbers are those numbers used for counting (as in "there are ''six'' coins on the table") and total order, ordering (as in "this is the ''third'' largest city in the country"). In common mathematical terminology, w ...

natural numbers
can be expressed, can include all
true True most commonly refers to truth Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In everyday language, truth is typically ascribed to things that aim to represent reality or otherw ...

true
statements about them. As a result, some domains of knowledge cannot be formalized, accurately and completely, as mathematical theories. (Here, formalizing accurately and completely means that all true propositions—and only true propositions—are derivable within the mathematical system.) This limitation, however, in no way precludes the construction of mathematical theories that formalize large bodies of scientific knowledge.


Underdetermination

A theory is ''underdetermined'' (also called ''indeterminacy of data to theory'') if a rival, inconsistent theory is at least as consistent with the evidence. Underdetermination is an
epistemological Epistemology (; ) is the branch of philosophy concerned with knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. The usual test for a statement of fact ...

epistemological
issue about the relation of
evidence Evidence for a proposition In logic and linguistics, a proposition is the meaning of a declarative sentence (linguistics), sentence. In philosophy, "Meaning (philosophy), meaning" is understood to be a non-linguistic entity which is shared by a ...

evidence
to conclusions. A theory that lacks supporting evidence is generally, more properly, referred to as a
hypothesis A hypothesis (plural hypotheses) is a proposed explanation An explanation is a set of statements usually constructed to describe a set of facts which clarifies the causes, context Context may refer to: * Context (language use), the rel ...
.


Intertheoretic reduction and elimination

If a new theory better explains and predicts a phenomenon than an old theory (i.e., it has more
explanatory power Explanatory power is the ability of a hypothesis or theory A theory is a reason, rational type of abstraction, abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often ass ...
), we are
justified Justified may refer to: * Justified (album), ''Justified'' (album), an album by Justin Timberlake * Justified (song), "Justified" (song), a single by Kacey Musgraves * Justified (TV series), ''Justified'' (TV series), an American television drama ...
in believing that the newer theory describes reality more correctly. This is called an ''intertheoretic reduction'' because the terms of the old theory can be reduced to the terms of the new one. For instance, our historical understanding about ''sound'', "light" and ''heat'' have been reduced to ''wave compressions and rarefactions'', ''electromagnetic waves'', and ''molecular kinetic energy'', respectively. These terms, which are identified with each other, are called ''intertheoretic identities.'' When an old and new theory are parallel in this way, we can conclude that the new one describes the same reality, only more completely. When a new theory uses new terms that do not reduce to terms of an older theory, but rather replace them because they misrepresent reality, it is called an ''intertheoretic elimination.'' For instance, the
obsolete scientific theory In Science#History, science, a theory is superseded when a scientific consensus once widely accepted it, but current science considers it inadequate, incomplete, or debunked (i.e., wrong). Such labels do not cover protoscience, protoscientific o ...
that put forward an understanding of heat transfer in terms of the movement of caloric fluid was eliminated when a theory of heat as energy replaced it. Also, the theory that
phlogiston The phlogiston theory is a superseded scientific theory that postulated the existence of a fire-like element called phlogiston () contained within combustible bodies and released during combustion Combustion, or burning, is a high-temperature ex ...
is a substance released from burning and rusting material was eliminated with the new understanding of the reactivity of oxygen.


Versus theorems

Theories are distinct from
theorem In mathematics, a theorem is a statement (logic), statement that has been Mathematical proof, proved, or can be proved. The ''proof'' of a theorem is a logical argument that uses the inference rules of a deductive system to establish that the the ...
s. A ''theorem'' is derived deductively from
axiom An axiom, postulate or assumption is a statement that is taken to be truth, true, to serve as a premise or starting point for further reasoning and arguments. The word comes from the Greek ''axíōma'' () 'that which is thought worthy or fit' o ...

axiom
s (basic assumptions) according to a
formal system A formal system is an used for inferring theorems from axioms according to a set of rules. These rules, which are used for carrying out the inference of theorems from axioms, are the logical calculus of the formal system. A formal system is essen ...
of rules, sometimes as an end in itself and sometimes as a first step toward being tested or applied in a concrete situation; theorems are said to be true in the sense that the conclusions of a theorem are logical consequences of the axioms. ''Theories'' are abstract and conceptual, and are supported or challenged by observations in the world. They are '
rigor Rigour (British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codification of grammar and usage ...
ously tentative', meaning that they are proposed as true and expected to satisfy careful examination to account for the possibility of faulty inference or incorrect observation. Sometimes theories are incorrect, meaning that an explicit set of observations contradicts some fundamental objection or application of the theory, but more often theories are corrected to conform to new observations, by restricting the class of phenomena the theory applies to or changing the assertions made. An example of the former is the restriction of classical mechanics to phenomena involving macroscopic length scales and particle speeds much lower than the speed of light.


The theory-practice gap

Theory is often distinguished from practice. The question of whether theoretical models of work are relevant to work itself is of interest to scholars of professions such as
medicine Medicine is the science Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity, awareness, or understanding of someone or something, such as facts ( descriptive knowledge), skills (proced ...

medicine
,
engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range of more speciali ...

engineering
, and
law Law is a system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment, is described by its bounda ...
, and
management Management (or managing) is the administration of an organization An organization, or organisation (Commonwealth English The use of the English language English is a West Germanic languages, West Germanic language first spok ...

management
. This gap between theory and practice has been framed as a
knowledge transfer Knowledge transfer refers to sharing or disseminating of knowledge and providing inputs to problem solving Problem solving consists of using generic or ad hoc Ad hoc is a List of Latin phrases, Latin phrase meaning literally 'to this'. I ...

knowledge transfer
where there is a task of translating research knowledge to be application in practice, and ensuring that practictioners are made aware of it academics have been criticized for not attempting to transfer the knowledge they produce to practitioners. Another framing supposes that theory and knowledge seek to understand different problems and model the world in different words (using different
ontologies In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Algor ...

ontologies
and ) . Another framing says that research does not produce theory that is relevant to practice. In the context of management, Van de Van and Johnson propose a form of engaged scholarship where scholars examine problems that occur in practice, in an
interdisciplinary Interdisciplinarity or interdisciplinary studies involves the combination of two or more academic disciplines into one activity (e.g., a research project). It draws knowledge from several other fields like sociology, anthropology, psychology, ...
fashion, producing results that create both new practical results as well as new theoretical models, but targeting theoretical results shared in an academic fashion. They use a metaphor of "arbitrage" of ideas between disciplines, distinguishing it from collaboration.


Scientific

In science, the term "theory" refers to "a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through
observation Observation is the active acquisition of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defines both its essence and the nature of its characteristics. Th ...

observation
and
experiment An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into Causality, cause-and-effect by demonstrating what outcome oc ...

experiment
."AAAS Evolution Resources
/ref> Theories must also meet further requirements, such as the ability to make
falsifiable In the philosophy of science, a theory is falsifiable if it is contradicted by ''possible observations''—i.e., by any observations that can be described in the language of the theory, which must have a conventional empirical interpretation. ...
predictions with consistent accuracy across a broad area of scientific inquiry, and production of strong evidence in favor of the theory from multiple independent sources (
consilience In science and history, consilience (also convergence of evidence or concordance of evidence) is the principle that evidence from independent, unrelated sources can "converge" on strong conclusions. That is, when multiple sources of evidence are i ...
). The strength of a scientific theory is related to the diversity of phenomena it can explain, which is measured by its ability to make
falsifiable In the philosophy of science, a theory is falsifiable if it is contradicted by ''possible observations''—i.e., by any observations that can be described in the language of the theory, which must have a conventional empirical interpretation. ...
predictions frame, '' The Old Farmer's Almanac'' is famous in the US for its (not necessarily accurate) long-range weather predictions. A prediction (Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the ...
with respect to those phenomena. Theories are improved (or replaced by better theories) as more evidence is gathered, so that accuracy in prediction improves over time; this increased accuracy corresponds to an increase in scientific knowledge. Scientists use theories as a foundation to gain further scientific knowledge, as well as to accomplish goals such as inventing
technology Technology ("science of craft", from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. I ...

technology
or curing
diseases A disease is a particular abnormal condition that negatively affects the structure or function (biology), function of all or part of an organism, and that is not due to any immediate external injury. Diseases are often known to be medical ...
.


Definitions from scientific organizations

The
United States National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and operated for a ...
defines scientific theories as follows:
The formal scientific definition of "theory" is quite different from the everyday meaning of the word. It refers to a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence. Many scientific theories are so well established that no new evidence is likely to alter them substantially. For example, no new evidence will demonstrate that the Earth does not orbit around the sun (heliocentric theory), or that living things are not made of cells (cell theory), that matter is not composed of atoms, or that the surface of the Earth is not divided into solid plates that have moved over geological timescales (the theory of plate tectonics) ... One of the most useful properties of scientific theories is that they can be used to make predictions about natural events or phenomena that have not yet been observed.
From the
American Association for the Advancement of Science The American Association for the Advancement of Science (AAAS) is an American international non-profit organization A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution ...
:
A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment. Such fact-supported theories are not "guesses" but reliable accounts of the real world. The theory of biological evolution is more than "just a theory." It is as factual an explanation of the universe as the atomic theory of matter or the germ theory of disease. Our understanding of gravity is still a work in progress. But the phenomenon of gravity, like evolution, is an accepted fact.
The term ''theory'' is not appropriate for describing
scientific models Scientific modelling is a scientific activity, the aim of which is to make a particular part or feature of the world easier to Understanding, understand, Definition, define, quantification (science), quantify, Visual system, visualize, or Simula ...
or untested, but intricate hypotheses.


Philosophical views

The
logical positivist Logical positivism, later called logical empiricism, and both of which together are also known as neopositivism, was a movement in Western philosophy Western philosophy refers to the philosophy, philosophical thought and work of the Western worl ...
s thought of scientific theories as ''deductive theories''—that a theory's content is based on some formal system of logic and on basic
axioms An axiom, postulate or assumption is a statement that is taken to be truth, true, to serve as a premise or starting point for further reasoning and arguments. The word comes from the Greek ''axíōma'' () 'that which is thought worthy or fit' or ...
. In a deductive theory, any sentence which is a
logical consequence Logical consequence (also entailment) is a fundamental concept Concepts are defined as abstract ideas A mental representation (or cognitive representation), in philosophy of mind Philosophy of mind is a branch of philosophy that studies ...
of one or more of the axioms is also a sentence of that theory. This is called the
received view of theoriesThe received view of theories is a position in the philosophy of science Philosophy of science is a branch of philosophy concerned with the foundations, methodology, methods, and implications of science. The central questions of this study conce ...
. In the
semantic view of theoriesThe semantic view of theories is a position in the philosophy of science Philosophy of science is a branch of philosophy concerned with the foundations, methodology, methods, and implications of science. The central questions of this study conce ...
, which has largely replaced the received view, theories are viewed as
scientific models Scientific modelling is a scientific activity, the aim of which is to make a particular part or feature of the world easier to Understanding, understand, Definition, define, quantification (science), quantify, Visual system, visualize, or Simula ...
. A
model In general, a model is an informative representation of an object, person or system. The term originally denoted the plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin ''modulus'', a measure. ...
is a logical framework intended to represent reality (a "model of reality"), similar to the way that a map is a graphical model that represents the territory of a city or country. In this approach, theories are a specific category of models that fulfill the necessary criteria. (See Theories as models for further discussion.)


In physics

In physics the term ''theory'' is generally used for a mathematical framework—derived from a small set of basic postulates (usually symmetries, like equality of locations in space or in time, or identity of electrons, etc.)—which is capable of producing experimental predictions for a given category of physical systems. One good example is classical electromagnetism, which encompasses results derived from gauge symmetry (sometimes called gauge invariance) in a form of a few equations called Maxwell's equations. The specific mathematical aspects of classical electromagnetic theory are termed "laws of electromagnetism", reflecting the level of consistent and reproducible evidence that supports them. Within electromagnetic theory generally, there are numerous hypotheses about how electromagnetism applies to specific situations. Many of these hypotheses are already considered adequately tested, with new ones always in the making and perhaps untested.


Regarding the term "theoretical"

Certain tests may be infeasible or technically difficult. As a result, theories may make predictions that have not been confirmed or proven incorrect. These predictions may be described informally as "theoretical". They can be tested later, and if they are incorrect, this may lead to revision, invalidation, or rejection of the theory.


Mathematical

In mathematics the use of the term ''theory'' is different, necessarily so, since mathematics contains no explanations of natural phenomena, ''per se'', even though it may help provide insight into natural systems or be inspired by them. In the general sense, a mathematical ''theory'' is a branch of or topic in mathematics, such as Set theory, Number theory, Group theory, Probability theory, Game theory, Control theory, Perturbation theory, etc., such as might be appropriate for a single textbook. In the same sense, but more specifically, the word ''theory'' is an extensive, structured collection of theorems, organized so that the proof of each theorem only requires the theorems and axioms that preceded it (no circular proofs), occurs as early as feasible in sequence (no postponed proofs), and the whole is as succinct as possible (no redundant proofs). Ideally, the sequence in which the theorems are presented is as easy to understand as possible, although illuminating a branch of mathematics is the purpose of textbooks, rather than the mathematical theory they might be written to cover.


Philosophical

A theory can be either ''descriptive'' as in science, or ''prescriptive'' (normative ethics, normative) as in philosophy. The latter are those whose subject matter consists not of empirical data, but rather of ideas. At least some of the elementary theorems of a philosophical theory are statements whose truth cannot necessarily be scientifically tested through empiricism, empirical observation. A field of study is sometimes named a "theory" because its basis is some initial set of assumptions describing the field's approach to the subject. These assumptions are the elementary theorems of the particular theory, and can be thought of as the axioms of that field. Some commonly known examples include set theory and number theory; however literary theory, critical theory, and music theory are also of the same form.


Metatheory

One form of philosophical theory is a ''metatheory'' or ''meta-theory''. A metatheory is a theory whose subject matter is some other theory or set of theories. In other words, it is a theory about theories. Statement (logic), Statements made in the metatheory about the theory are called metatheorems.


Political

A political theory is an ethics, ethical theory about the law and government. Often the term "political theory" refers to a general view, or specific ethic, political belief or attitude, thought about politics.


Jurisprudential

In social science, jurisprudence is the philosophical theory of law. Contemporary philosophy of law addresses problems internal to law and legal systems, and problems of law as a particular social institution.


Examples

Most of the following are scientific theories. Some are not, but rather encompass a body of knowledge or art, such as Music theory and Visual Arts Theories. * Anthropology: Carneiro's circumscription theory * Astronomy: Alpher–Bethe–Gamow paper, Alpher–Bethe–Gamow theory — B2FH paper, B2FH Theory — Copernican heliocentrism, Copernican theory — Giant impact hypothesis — Gravity#Newton's theory of gravitation, Newton's theory of gravitation — Hubble's law — Kepler's laws of planetary motion — Nebular hypothesis — Geocentric model, Ptolemaic theory * Cosmology: Big Bang, Big Bang Theory — Cosmic inflation — Loop quantum gravity — Superstring theory — Supergravity — Supersymmetric theory — Multiverse theory — Holographic principle — Quantum gravity — M-theory * Biology: Cell theory — Evolution — Germ theory * Chemistry: Molecule, Molecular theory — Kinetic theory of gases — Molecular orbital theory — Valence bond theory — Transition state theory — RRKM theory — Chemical graph theory — Flory–Huggins solution theory — Marcus theory — Lewis theory (successor to Brønsted–Lowry acid–base theory) — HSAB theory — Debye–Hückel theory — Thermodynamic theory of polymer elasticity — Reptation theory — Polymer field theory — Møller–Plesset perturbation theory — density functional theory — Frontier molecular orbital theory — Polyhedral skeletal electron pair theory — Baeyer strain theory — Qtaim, Quantum theory of atoms in molecules — Collision theory — Ligand field theory (successor to Crystal field theory) — Variational transition-state theory — Benson group increment theory — Specific ion interaction theory * Climatology: Climate variability and change, Climate change theory (general study of climate changes) and Human impact on the environment, anthropogenic climate change (ACC)/ global warming (AGW) theories (due to human activity) * Economics: Macroeconomic theory — Microeconomic theory — Law of Supply and demand * Education: Constructivist theory — Critical pedagogy theory — Education theory — Multiple intelligence theory — Progressive education theory * Engineering: Circuit theory — Control theory — Signal theory — Systems theory — Information theory * Film: Film theory, Film Theory * Geology: Plate tectonics * Humanities: Critical theory * Jurisprudence or 'Legal theory': Natural law — Legal positivism — Legal realism — Critical legal studies * Law: see Jurisprudence; also Case theory (in law), Case theory * Linguistics: X-bar theory — Government and Binding — Principles and parameters — Universal grammar * Literature: Literary theory * Mathematics: Approximation theory — Arakelov theory — Asymptotic theory — Bifurcation theory — Catastrophe theory — Category theory — Chaos theory — Choquet theory — Coding theory — Combinatorial game theory — Computability theory — Computational complexity theory — Deformation theory — Dimension theory — Ergodic theory — Field theory (mathematics), Field theory — Galois theory — Game theory — Graph theory — Group theory — Hodge theory — Homology theory — Homotopy theory — Ideal theory — Intersection theory — Invariant theory — Iwasawa theory — K-theory — KK-theory — Knot theory — L-theory — Lie theory — Littlewood–Paley theory — Matrix (mathematics), Matrix theory — Measure theory — Model theory — Morse theory — Nevanlinna theory — Number theory — Obstruction theory — Operator theory — PCF theory — Perturbation theory — Potential theory — Probability theory — Ramsey theory — Rational choice theory — Representation theory — Ring theory — Set theory — Shape theory (mathematics), Shape theory — Small cancellation theory — Spectral theory — Stability theory — Stable theory — Sturm–Liouville theory — Twistor theory * Music: Music theory * Philosophy: Proof theory — Speculative reason — Truth, Theory of truth — Type theory — Value theory — Virtue theory * Physics: Acoustic theory — Antenna theory — Atomic theory — BCS theory — Dirac hole theory — Dynamo theory — Landau theory — M-theory — Perturbation theory (quantum mechanics), Perturbation theory — Theory of relativity (successor to classical mechanics) — Quantum field theory — Scattering theory — String theory — Quantum information theory * Psychology: Theory of mind — Cognitive dissonance theory — Attachment theory — Object permanence — Poverty of stimulus — Attribution theory — Self-fulfilling prophecy — Stockholm syndrome * Public Budgeting: Incrementalism — Zero-based budgeting * Public Administration: Organizational theory * Semiotics
Intertheoricity

Transferogenesis
* Sociology: Critical theory (Frankfurt School), Critical theory — Engaged theory — Social theory — Sociological theory - Social capital theory * Statistics: Extreme value theory * Theatre#Theories of theatre, Theatre: Performance studies, Performance theory * Visual Art: Aesthetics — Art teaching, Art educational theory — Architecture — Composition (visual arts), Composition — Anatomy — Color theory — Perspective (graphical), Perspective — Visual perception — Geometry — Manifolds * Other: Obsolete scientific theories


See also

* Falsifiability * Hypothesis testing * Physical law * Predictive power * Testability * Theoretical definition


Notes


References


Citations


Sources

* Davidson Reynolds, Paul (1971). ''A primer in theory construction''. Boston: Allyn and Bacon. * Guillaume, Astrid (2015). « Intertheoricity: Plasticity, Elasticity and Hybridity of Theories. Part II: Semiotics of Transferogenesis », in ''Human and Social studies'', Vol.4, N°2 (2015), éd.Walter de Gruyter, Boston, Berlin, pp. 59–77. * Guillaume, Astrid (2015). « The Intertheoricity : Plasticity, Elasticity and Hybridity of Theories », in ''Human and Social studies'', Vol.4, N°1 (2015), éd.Walter de Gruyter, Boston, Berlin, pp. 13–29. * Hawking, Stephen (1996). ''A Brief History of Time'' (Updated and expanded ed.). New York: Bantam Books, p. 15. * * . * Karl Popper, Popper, Karl (1963), ''Conjectures and Refutations'', Routledge and Kegan Paul, London, UK, pp. 33–39. Reprinted in Theodore Schick (ed., 2000), ''Readings in the Philosophy of Science'', Mayfield Publishing Company, Mountain View, California, USA, pp. 9–13. * Zima, Peter V. (2007). "What is theory? Cultural theory as discourse and dialogue". London: Continuum (translated from: Was ist Theorie? Theoriebegriff und Dialogische Theorie in der Kultur- und Sozialwissenschaften. Tübingen: A. Franke Verlag, 2004).


External links


"How science works: Even theories change"
''Understanding Science'' by the University of California Museum of Paleontology.

{{Authority control Theories, Abstraction Conceptual systems Inductive reasoning Ontology