# theory
## English
### Etymology

From Middle French théorie, from Late Latin theōria, from Ancient Greek θεωρία (theōría, “contemplation, divine perspective, speculation, a looking at, a seeking”), from θεωρέω (theōréō, “I look at, view, see, consider, examine”), from θεωρός (theōrós, “spectator”), from θέα (théa, “view, perspective, sight”) + ὁράω (horáō, “I see, look”) [i. e. θέαν ὁράω (théan horáō, “see, look at a view; survey + genitive”)].

### Pronunciation

* (Received Pronunciation, General Australian) IPA: /ˈθɪə.ɹi/
* (General American) IPA: /ˈθɪ.ɹi/, /ˈθi.ə.ɹi/
** Audio (US):(file)
* (US, without the mirror–nearer merger) IPA: /ˈθɪɚ.i/, /ˈθi.ɹi/
* (Scotland) IPA: /ˈθi.ɹɪ/, /ˈθi.ɹe/
* (New Zealand) IPA: /ˈθiə.ɹi/
* (East Anglia, cheer–chair merger) IPA: /ˈθɛː.ɹi/
    Rhymes: -ɪəɹi, -iːəɹi

### Noun

theory (countable and uncountable, plural theories)
* A description of an event or system that is considered to be accurate.
** 1646, Thomas Browne, Pseudodoxia Epidemica, VII.19:As they encrease the hatred of vice in some, so doe they enlarge the theory of wickednesse in all.
* (sciences) A coherent statement or set of ideas that explains observed facts or phenomena and correctly predicts new facts or phenomena not previously observed, or which sets out the laws and principles of something known or observed; a hypothesis confirmed by observation, experiment etc. [from 17th c.]
** 1843, John Stuart Mill, ""A System of Logic, Ratiocinative and Inductive, ..., Bk V, Ch 7:
    In its most proper acceptation, theory means the completed result of philosophical induction from experience.
** 1990, Tony Bennett, Outside Literature, page 139:Does this mean, then, that there can be no such thing as a theory of literature?
** 2002 May 23, Duncan Steel, The Guardian:It was only when Einstein's theory of relativity was published in 1915 that physicists could show that Mercury's "anomaly" was actually because Newton's gravitational theory was incomplete.
** 2003, Bill Bryson, A Short History of Nearly Everything, BCA, page 118:The world would need additional decades [...] before the Big Bang would begin to move from interesting idea to established theory.
** 2009, Richard Dawkins, The Greatest Show On Earth: The Evidence for Evolution, Bantam, page 10:Scientists and creationists are understanding the word "theory" in two very different senses. Evolution is a theory in the same sense as the heliocentric theory. In neither case should the word "only" be used, as in "only a theory".
** 2012 January, Michael Riordan, “Tackling Infinity”, in American Scientist‎, volume 100, number 1, archived from the original on 30 April 2013, page 86:Some of the most beautiful and thus appealing physical theories, including quantum electrodynamics and quantum gravity, have been dogged for decades by infinities that erupt when theorists try to prod their calculations into new domains. Getting rid of these nagging infinities has probably occupied far more effort than was spent in originating the theories.
* (uncountable) The underlying principles or methods of a given technical skill, art etc., as opposed to its practice. [from 17th c.]
** 1998, Elizabeth Souritz, The Great History of Russian Ballet:Lopukhov wrote a number of books and articles on ballet theory, as well as his memoirs.
* (mathematics) A field of study attempting to exhaustively describe a particular class of constructs. [from 18th c.]
    Knot theory classifies the mappings of a circle into 3-space.
** 1999, Wes DeMott, Vapors:It's just a theory I have, and I wonder if women would agree. But don't men say a lot about themselves when a short-skirted woman slides out of a car or chair?
** 2003 June 21, Sean Coughlan, The Guardian:The theory is that by stripping costs to the bone, they are able to offer ludicrously low fares.
* (countable, logic) A set of axioms together with all statements derivable from them; or, a set of statements which are deductively closed. Equivalently, a formal language plus a set of axioms (from which can then be derived theorems). The statements may be required to all be bound (i.e., to have no free variables).
    A theory is consistent if it has a model.
* (obsolete) Mental conception; reflection, consideration. [16th–18th c.]
* (informal) A hypothesis or conjecture. [from 18th c.]

#### Usage notes

In scientific discourse, the informal sense of “unsubstantiated statement or idea” is discouraged (with hypothesis or conjecture preferred), due to unintentional ambiguity and intentional equivocation with the sense “well-developed statement or structure”.

#### Synonyms

* See also Thesaurus:supposition

#### Hyponyms

* AAK-theory
* AAK theory
* abrupt appearance theory
* abstinence theory
* abstract analytic number theory
* acoustic theory
* action theory
* activity theory
* additive number theory
* Ahlfors theory
* algebraic graph theory
* algebraic K-theory
* algebraic number theory
* algorithmic information theory
* algorithmic number theory
* analytic number theory
* antenna theory
* approximation theory
* aquatic ape theory
* arbitrage pricing theory
* AR theory
* assemblage theory
* atomic theory
* attainable region theory
* attribution theory
* auction theory
* Auslander-Reiten theory
* auteur theory
* autotheory
* BCS theory
* bifurcation theory
* binary theory
* Bohr theory
* bow-wow theory
* bowwow theory
* broken windows theory
* broken window theory
* burnt toast theory
* cable theory
* catastrophe theory
* category theory
* cell theory
* chaos theory
* character theory
* Chern-Simons theory
* choice theory
* circuit theory
* cobweb theory
* cockroach theory
* coding theory
* coincidence theory
* collision theory
* communication accommodation theory
* complexity theory
* computability theory
* computational complexity theory
* computational number theory
* computation theory
* conspiracy theory
* continuum theory
* control theory
* coorbit theory
* cosmological perturbation theory
* counterpart theory
* countertheory
* critical race theory
* critical theory
* crystal field theory
* cuckoo theory
* cultivation theory
* cybertheory
* dead internet theory
* de Broglie-Bohm theory
* Debye-Hückel theory
* decision theory
* dependency theory
* ding-dong theory
* divine command theory
* DLVO theory
* domain theory
* domino theory
* Donaldson-Thomas theory
* Dow theory
* dual-coding theory
* dynamo theory
* ecotheory
* e-learning theory
* emission theory
* endosymbiotic theory
* epitheory
* ergodic theory
* estimation theory
* ethnotheory
* evolutionary theory
* extreme value theory
* fast leg theory
* field theory
* fish-hook theory
* flypaper theory
* Fredholm theory
* fringe theory
* Galois theory
* game theory
* gap theory
* gauge theory
* gender theory
* germ theory
* germ theory of disease
* giant impact theory
* global workspace theory
* grand theory
* grand unification theory
* grand unified theory
* graph theory
* greater fool theory
* great man theory
* great replacement theory
* Green Lantern theory
* grounded theory
* group theory
* Heim theory
* hemline theory
* Hodge theory
* homotopy theory
* horseshoe theory
* iceberg theory
* information theory
* inter-universal Teichmüller theory
* invariant theory
* ironic process theory
* James-Lange theory
* Kaluza-Klein theory
* kinetic theory of gases
* knot theory
* K-theory
* labor theory of value
* labor-value theory
* labor value theory
* labour theory of value
* labour-value theory
* labour value theory
* lattice theory
* leg theory
* lesbian dance theory
* ligand field theory
* literary theory
* LQG theory
* lunar theory
* macrotheory
* madman theory
* measure theory
* metatheory
* microtheory
* minitheory
* mirror theory
* model theory
* module theory
* molecular orbital theory
* Morse theory
* motor theory
* M-theory
* music theory, musical theory
* Nevanlinna theory
* nontheory
* novelty theory
* nudge theory
* number theory
* operator theory
* opponent-process theory
* optimality theory
* orange peel theory
* Out of India theory
* particle theory
* pattern theory
* Peccei-Quinn theory
* perceptual control theory
* percolation theory
* perturbation theory
* phlogiston theory
* pooh-pooh theory
* potential theory
* probability theory
* proof theory
* prototype theory
* psychotheory
* quantity theory of money
* quantum field theory
* quantum information theory
* quantum theory
* quark theory
* queer theory
* queueing theory
* r/K selection theory
* Ramsey theory
* rational choice theory
* recapitulation theory
* recursion theory
* Regge theory
* renewal theory
* replacement theory
* representation theory
* rimland theory
* ring theory
* ruin theory
* Sahara pump theory
* sandwich theory
* scheme theory
* seduction theory
* set theory
* sheaf theory
* sieve theory
* signal theory
* situation theory
* size theory
* Skopos theory
* social theory
* spectral theory
* spoon theory
* standard theory
* standpoint theory
* steady state theory
* stoned ape theory
* stone tape theory
* Strauss-Howe generational theory
* string theory
* Sturm-Liouville theory
* subtheory
* supposition theory
* swollen assets theory
* synthetic theory
* systems theory
* ta-ta theory
* terrain theory
* theory of abrupt appearance
* theory of everything
* theory of games
* theory of gravity
* theory of mind
* theory of music
* theory of musical equilibration
* theory of relativity
* theory of truth
* theory of value
* Theory X
* Theory Y
* thing theory
* toy theory
* transcendental number theory
* type theory
* unexpected red theory
* value theory
* veneer theory
* virtue theory
* vortex theory
* wave theory
* Wheeler-Feynman absorber theory
* white inflation theory
* white replacement theory
* X-bar theory
* X′ theory
* Yang-Mills theory
* yo-heave-ho theory
* yo-he-ho theory
* Zermelo-Fraenk set theory
* Zermelo set theory

#### Meronyms

* (in logic): axioms

#### Holonyms

* (in logic): formal system

#### Derived terms

* intertheory
* in theory
* intratheory
* theoretic
* theorist
* theorycel
* theorycraft
* theoryhead
* theoryism
* theory-laden
* theoryless
* time-preference theory of interest

#### Related terms

* theorem
* theoretical
* theorise, theorize

#### Translations

    The translations below need to be checked and inserted above into the appropriate translation tables. See instructions at Wiktionary:Entry layout § Translations.

### See also

* axiom
* postulate
* proposition

### References

* “theory”, in OneLook Dictionary Search.
* theory in Keywords for Today: A 21st Century Vocabulary, edited by The Keywords Project, Colin MacCabe, Holly Yanacek, 2018.
* "theory" in Raymond Williams, Keywords (revised), 1983, Fontana Press, page 316.
* William Dwight Whitney, Benjamin E[li] Smith, editors (1911), “theory”, in The Century Dictionary […], New York, N.Y.: The Century Co., →OCLC.

### Anagrams

* Yother, thyreo-