Theory

For theories in science, seeScientific theory.For other uses, seeTheory (disambiguation).

Atheoryis arationaltype ofabstract thinkingabout aphenomenon,or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes asobservational studyor research. Theories may bescientific,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 hownatureworks. The word has its roots inancient Greek,but in modern use it has taken on several related meanings.

In modern science, the term "theory" refers toscientific theories,a well-confirmed type of explanation ofnature,made in a wayconsistentwith thescientific method,and fulfilling thecriteriarequired bymodern science.Such theories are described in such a way that scientific tests should be able to provideempiricalsupport for it, orempiricalcontradiction ( "falsify") 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 wordhypothesis).Scientific theories are distinguished from hypotheses, which are individual empiricallytestableconjectures,and fromscientific laws,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 abody of knowledge,which may or may not be associated with particular explanatorymodels.To theorize is to develop this body of knowledge.

The word theory or "in theory" is sometimes used outside of science to refer to something which the speaker did not experience or test before.In science, this same concept is referred to as ahypothesis,and the word "hypothetically" is used both inside and outside of science. In its usage outside of science, the word "theory" is very often contrasted to "practice"(from Greekpraxis,πρᾶξις) a Greek term fordoing,which is opposed to theory.A "classical example" of the distinction between "theoretical" and "practical" uses the discipline of medicine:medical theoryinvolves trying to understand thecausesand 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 wordtheoryderives from a technical term in philosophy inAncient Greek.As an everyday word,theoria,θεωρία,meant "looking at, viewing, beholding", but in more technical contexts it came to refer tocontemplativeorspeculativeunderstandings ofnatural things,such as those ofnatural philosophers,as opposed to more practical ways of knowing things, like that of skilled orators or artisans.English-speakers have used the wordtheorysince at least the late 16th century.Modern uses of the wordtheoryderive from the original definition, but have taken on new shades of meaning, still based on the idea of a theory as a thoughtful andrationalexplanation of the generalnatureof things.

Although it has more mundane meanings in Greek, the wordθεωρίαapparently developed special uses early in the recorded history of theGreek language.In the bookFrom Religion to Philosophy,Francis Cornfordsuggests that theOrphicsused the wordtheoriato mean "passionate sympathetic contemplation".Pythagoraschanged 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 wordtheorythe 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 withpraxisor 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 asnature,so it has no human aim apart from itself and the knowledge it helps create. On the other hand,praxisinvolves 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 ofpraxisor doing.

Formality

Main article:Theory (mathematical logic)

Theories areanalyticaltools forunderstanding,explaining,and makingpredictionsabout a given subject matter. There are theories in many and varied fields of study, including the arts and sciences. A formal theory issyntacticin nature and is only meaningful when given asemanticcomponent by applying it to some content (e.g.,factsand relationships of the actual historical world as it is unfolding). Theories in various fields of study are often expressed innatural language,but can be constructed in such a way that their general form is identical to a theory as it is expressed in theformal languageofmathematical logic.Theories may be expressed mathematically, symbolically, or in common language, but are generally expected to follow principles ofrational thoughtorlogic.

Theory is constructed of a set ofsentencesthat are thought to be 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 someinterpretationof who "He" is and for that matter what a "terrible person" is under the theory.

Sometimes two theories have exactly the sameexplanatory powerbecause they make the same predictions. A pair of such theories is called indistinguishable orobservationally equivalent,and the choice between them reduces to convenience or philosophical preference.

Theform of theoriesis studied formally in mathematical logic, especially inmodel theory.When theories are studied in mathematics, they are usually expressed in some formal language and their statements areclosedunder application of certain procedures calledrules of inference.A special case of this, an axiomatic theory, consists ofaxioms(or axiom schemata) and rules of inference. Atheoremis a statement that can be derived from those axioms by application of these rules of inference. Theories used in applications areabstractionsof observed phenomena and the resulting theorems provide solutions to real-world problems. Obvious examples includearithmetic(abstracting concepts of number),geometry(concepts of space), andprobability(concepts of randomness and likelihood).

Gödel's incompleteness theoremshows that no consistent,recursively enumerabletheory (that is, one whose theorems form a recursively enumerable set) in which the concept ofnatural numberscan be expressed, can include alltruestatements 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

Main article:Underdetermination

A theory isunderdetermined(also calledindeterminacy of data to theory) if a rival, inconsistent theory is at least as consistent with the evidence. Underdetermination is anepistemologicalissue about the relation ofevidenceto conclusions.

A theory that lacks supporting evidence is generally, more properly, referred to as ahypothesis.

Intertheoretic reduction and elimination

Main article:Intertheoretic reduction

If a new theory better explains and predicts a phenomenon than an old theory (i.e., it has moreexplanatory power), we arejustifiedin believing that the newer theory describes reality more correctly. This is called anintertheoretic reductionbecause the terms of the old theory can be reduced to the terms of the new one. For instance, our historical understanding aboutsound,lightandheathave been reduced towave compressions and rarefactions,electromagnetic waves,andmolecular kinetic energy,respectively. These terms, which are identified with each other, are calledintertheoretic 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 anintertheoretic elimination.For instance, theobsolete scientific theorythat put forward an understanding of heat transfer in terms of the movement ofcaloric fluidwas eliminated when a theory of heat as energy replaced it. Also, the theory thatphlogistonis a substance released from burning and rusting material was eliminated with the new understanding of the reactivity of oxygen.

Versus theorems

Theories are distinct fromtheorems.Atheoremisderiveddeductively fromaxioms(basic assumptions) according to aformal systemof 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.Theoriesare abstract and conceptual, and are supported or challenged by observations in the world. They are 'rigorouslytentative', 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.

Theory–practice relationship

See also:Praxis (process)

Theory is often distinguished from practice or praxis. The question of whether theoretical models of work are relevant to work itself is of interest to scholars of professions such as medicine, engineering, law, and management.

The gap between theory and practice has been framed as aknowledge transferwhere there is a task of translating research knowledge to be application in practice, and ensuring that practitioners 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 differentontologiesandepistemologies). 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 ofengaged scholarshipwhere scholars examine problems that occur in practice, in aninterdisciplinaryfashion, 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

Main article:Scientific theory

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 beenrepeatedly confirmedthroughobservationand experiment. "Theories must also meet further requirements, such as the ability to makefalsifiablepredictions 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).

The strength of a scientific theory is related to the diversity of phenomena it can explain, which is measured by its ability to makefalsifiablepredictionswith 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 or curing diseases.

Definitions from scientific organizations

TheUnited States National Academy of Sciencesdefines 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 theAmerican Association for the Advancement of Science:

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 termtheoryis not appropriate for describingscientific modelsor untested, but intricate hypotheses.

Philosophical views

Thelogical positiviststhought of scientific theories asdeductive theories—that a theory's content is based on someformal systemof logic and on basicaxioms.In a deductive theory, any sentence which is alogical consequenceof one or more of the axioms is also a sentence of that theory.This is called thereceived view of theories.

In thesemantic view of theories,which has largely replaced the received view,theories are viewed asscientific models.Amodelis 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. (SeeTheories as modelsfor further discussion.)

In physics

Inphysicsthe termtheoryis generally used for a mathematical framework—derived from a small set of basicpostulates(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 isclassical electromagnetism,which encompasses results derived fromgauge symmetry(sometimes called gauge invariance) in a form of a few equations calledMaxwell'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

See also:List of mathematical theories

In mathematics, the termtheoryis used differently than its use in science ─ necessarily so, since mathematics contains no explanations of natural phenomenaper se,even though it may help provide insight into natural systems or be inspired by them. In the general sense, amathematical theoryis a branch of mathematics devoted to some specific topics or methods, such asset theory,number theory,group theory,probability theory,game theory,control theory,perturbation theory,etc., such as might be appropriate for a single textbook.

Inmathematical logic,atheoryhas a related but different sense: it is the collection of the theorems that can be deduced from a given set ofaxioms,given a given set ofinference rules.

Philosophical

Main article:Philosophical theory

A theory can be eitherdescriptiveas in science, orprescriptive(normative) as in philosophy.The latter are those whose subject matter consists not of empirical data, but rather ofideas.At least some of the elementary theorems of a philosophical theory are statements whose truth cannot necessarily be scientifically tested throughempirical 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 includeset theoryandnumber theory;howeverliterary theory,critical theory,andmusic theoryare also of the same form.

Metatheory

Main article:Metatheory

One form of philosophical theory is ametatheoryormeta-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.Statementsmade in the metatheory about the theory are calledmetatheorems.

Political

Main article:Political theory

A political theory is anethicaltheory 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

Main articles:JurisprudenceandLaw

In social science,jurisprudenceis 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 theory—
  • B²FH Theory—
  • Copernican theory—
  • Newton's theory of gravitation—
  • Hubble's law—
  • Kepler's laws of planetary motionPtolemaic theory
• Biology:
  • Cell theory—
  • Chemiosmotic theory—
  • Evolution—
  • Germ theory—
  • Symbiogenesis
• Chemistry:
  • 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 toBrønsted–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—
  • Quantum theory of atoms in molecules—
  • Collision theory—
  • Ligand field theory(successor toCrystal field theory) —
  • Variational transition-state theory—
  • Benson group increment theory—
  • Specific ion interaction theory
• Climatology:
  • Climate change theory(general study of climate changes)
  • anthropogenicclimate change(ACC)/
  • anthropogenicglobal warming(AGW) theories (due to human activity)
• Computer Science:
  • Automata theory—
  • Queueing theory
• Cosmology:
  • Big BangTheory —
  • Cosmic inflation—
  • Loop quantum gravity—
  • Superstring theory—
  • Supergravity—
  • Supersymmetric theory—
  • Multiverse theory—
  • Holographic principle—
  • Quantum gravity—
  • M-theory
• Economics:
  • Macroeconomic theory—
  • Microeconomic theory—
  • Law ofSupply 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
• Geology:
  • Plate tectonics
• Humanities:
  • Critical theory
• Jurisprudenceor 'Legal theory':
  • Natural law—
  • Legal positivism—
  • Legal realism—
  • Critical legal studies
• Law:see Jurisprudence; alsoCase 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—
  • Galois theory—
  • Game theory—
  • Gauge 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 theory—
  • Measure theory—
  • Model theory—
  • Module theory—
  • Morse theory—
  • Nevanlinna theory—
  • Number theory—
  • Obstruction theory—
  • Operator theory—
  • Order theory—
  • PCF theory—
  • Perturbation theory—
  • Potential theory—
  • Probability theory—
  • Ramsey theory—
  • Rational choice theory—
  • Representation theory—
  • Ring theory—
  • Set theory—
  • Shape theory—
  • Small cancellation theory—
  • Spectral theory—
  • Stability theory—
  • Stable theory—
  • Sturm–Liouville theory—
  • Surgery theory—
  • Twistor theory—
  • Yang–Mills theory
• Music:
  • Music theory
• Philosophy:
  • Proof theory—
  • Speculative reason—
  • Theory of truth—
  • Type theory—
  • Value theory—
  • Virtue theory
• Physics:
  • Acoustic theory—
  • Antenna theory—
  • Atomic theory—
  • BCS theory—
  • Conformal field theory—
  • Dirac hole theory—
  • Dynamo theory—
  • Landau theory—
  • M-theory—
  • Perturbation theory—
  • Theory of relativity(successor toclassical mechanics) —
  • Gauge theory—
  • 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—
  • Engaged theory—
  • Social theory—
  • Sociological theory–
  • Social capitaltheory
• Statistics:
  • Extreme value theory
• Theatre:
  • Performance theory
• Visual Arts:
  • Aesthetics—
  • Art educational theory—
  • Architecture—
  • Composition—
  • Anatomy—
  • Color theory—
  • Perspective—
  • Visual perception—
  • Geometry—
  • Manifolds
• Other:
  • Obsolete scientific theories

See also

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

References

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 », inHuman 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 », inHuman 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.
• James, Paul(2006).Globalism, Nationalism, Tribalism: Bringing Theory Back In.London, England: Sage Publications.
• Matson, Ronald Allen, "Comparing scientific laws and theories",Biology,Kennesaw State University.
• Popper, Karl(1963),Conjectures and Refutations,Routledge and Kegan Paul, London, UK, pp. 33–39. Reprinted inTheodore 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).

Further reading

• Eisenhardt, K. M., & Graebner, M. E. (2007). Theory building from cases: Opportunities and challenges. Academy of management journal, 50(1), 25-32.

External links

• "How science works: Even theories change",Understanding Scienceby the University of California Museum of Paleontology.
• What is a Theory?