Definition of theory in US English:

theory

nounPlural theories

  • 1A 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’
    • ‘Evolutionary theories attempt to explain how the fact of evolution occurs.’
    • ‘No general theory explaining breeding dispersal has yet been formalized, but two main hypotheses have emerged.’
    • ‘No matter how hard we try to produce theories and hypotheses to explain the market, it will always prove to be unpredictable.’
    • ‘In geology, the theory of evolution could explain two agreed facts that had given the scriptural view of creation a hard time.’
    • ‘Pope John Paul II has already explained that the theory of evolution is not irreconcilable with the creation doctrine.’
    • ‘She neatly interweaves discussions of online behavior with social science theories that may explain some Internet phenomena.’
    • ‘He is regarded as the founder of the general functionalist theory of the social system.’
    • ‘Theories do not become facts; theories explain facts, and a well validated theory does not turn into something else; it remains a theory forever.’
    • ‘Do you think that Hume wanted a general theory of human nature to explain why human beings act, think, perceive and feel in all of the ways that we do?’
    • ‘Hypotheses and theories are generally based on objective inferences, unlike opinions, which are generally based on subjective influences.’
    • ‘In general, this theory attempts to explain when and how people adopt new behaviors.’
    • ‘But bundle theory is supposed to explain the structure of things on a metaphysical, not scientific level.’
    • ‘Social cognitive theory, ecological systems theory and cultural-historical theory have a contextual base.’
    • ‘Objections to the general theory of evolution are presented in both Darwin's conclusion and glossary of terms.’
    • ‘All makers of monolithic theories want their theories to explain everything, and they want them to be strong and relatively simple.’
    • ‘That was before he started questioning whether Darwin's theory of evolution fully explained life on earth.’
    • ‘In 1915, with his theory of general relativity, Einstein extended this hypothesis to include gravitation.’
    • ‘Eventually Einstein's general relativity theory explained the phenomenon in terms of a distortion of the fabric of space by the Sun's gravity.’
    • ‘Religious-mystical theories, biological theories and socio-historical theories explain the existence of the caste system.’
    • ‘Instead, he now requires them to be able to explain the scientific theory of evolution.’
    hypothesis, thesis, conjecture, supposition, speculation, postulation, postulate, proposition, premise, surmise, assumption, presumption, presupposition, notion, guess, hunch, feeling, suspicion
    principles, ideas, concepts
    View synonyms
    1. 1.1 A set of principles on which the practice of an activity is based.
      ‘a theory of education’
      ‘music theory’
      • ‘In an interview with this magazine, he offered some of his best thinking on the theory and practice of managing knowledge.’
      • ‘The principles link theory and practice, they translate the theoretical positions into the language of military practice.’
      • ‘The author proposes that only through a knowledge of music theory and practice can one understand the origins of modern science.’
      • ‘Whatever it comes to be called, we know it as the discipline devoted to the theory and practice of writing and teaching writing.’
      • ‘If the argument of this essay is valid, then we face a major task of reassessment of much of the theory and practice of Christian spirituality.’
      • ‘On the debit side it seems we don't always have the players with the required levels of skill to carry the theory into practice.’
      • ‘However, in both the Christian and the Islamic worlds, it was the theory, not the practice of music that held sway as an intellectual pursuit.’
      • ‘The problem is that it's a lot harder to put the theory into practice.’
      • ‘Nowadays it's not so common for writers to put their theory into practice!’
      • ‘Really good trainers know it's important to make you perform each task - but how many of them put the theory into practice?’
      • ‘And he was a rare example of a scholar who put his theories into practice, both inside and outside the classroom.’
      • ‘The journal provides a forum for the discussion of the theory and practice of drama and theatre education.’
      • ‘Cayley's book was written at a time when the rehabilitative theory and practice of prisons, parole and other measures were under attack from the right.’
      • ‘Much is known about the biological effects of radiation, and the theory and practice of human radiation protection has been developed in a systematic way.’
      • ‘His research spans economic history, methodology, and the theory and practice of interdisciplinarity.’
      • ‘What follows foregrounds just some of the implications of biomedicine for the theory and practice of public mental health.’
      • ‘A simple theoretical construct underlies the theory and practice of counterinsurgency warfare.’
      • ‘But they also learn the theory and practice of guerrilla warfare.’
      • ‘It was a residential programme which accepted successful applicants for two years of training in the theory of education and practice of teaching.’
      • ‘But theory and practice never seem to square properly with each other.’
      doctrine, dogma, teaching, principle, ethic, creed, credo, thesis, ideology, idea, ideal, position
      View synonyms
    2. 1.2 An idea used to account for a situation or justify a course of action.
      ‘my theory would be that the place has been seriously mismanaged’
      • ‘Those are wonderful theories and of course, no one can ever prove them right or wrong.’
      • ‘That's only a theory, of course, but one which I'm willing to defend.’
      • ‘He took a step towards me, his eyes searching, ‘I have my theories, of course.’’
      • ‘He replied that polygenists in the United States had in fact used their theories to justify slavery.’
      • ‘Of course, the simplest theory is that he did so well because he was a very good swimmer!’
      • ‘His theory does not adequately account for the dual powers of divine conflagration and divine grace.’
      • ‘And of course my personal theory on this is that women, who do childbirth after all, can handle a lot more pain.’
      • ‘In any case, much qualitative research entails the testing of theories in the course of the research process.’
      • ‘It may be that in a federal constitutional situation your theory is correct.’
      • ‘The experts laugh at my theories of course until I point out that they help me manage and live with the pain.’
      • ‘And of course there is the theory that the dinosaurs were wiped out by a mega-tsunami caused by an asteroid.’
      • ‘There are, officers say, five theories which could account for his death.’
      • ‘There is no evidence to support such theories, of course, but hey - since when do liberals need evidence?’
      • ‘Besides the miraculous escape, the theory also accounts for the waters flowing back to destroy the Pharaoh's army that chased Moses and the Jews.’
      • ‘There are many theories about Vietnam of course.’
      • ‘My theory, of course, is that these were all written by one person using various pseudonyms.’
      • ‘And of course, as the theory of nuclear deterrence ordains, India and Pakistan, being nuclear powers, would never go to war again.’
      • ‘I have no other proof than logic, and so far events have justified my theory.’
      • ‘Blake was beginning to develop a new theory to account for what seemed to be going on around him.’
      • ‘Of course, the theory is very attractive, and leads many medical doctors and public health officials to believe we should vaccinate more often and against many more diseases.’
      opinion, point of view, viewpoint, belief, judgement, reckoning, way of thinking, thinking, thought, notion, idea, conviction, persuasion, attitude, feeling, sentiment, impression, concept, conception, hypothesis, thesis, estimate, estimation, conclusion, verdict
      View synonyms
    3. 1.3Mathematics A collection of propositions to illustrate the principles of a subject.
      • ‘Bolzano's theories of mathematical infinity anticipated Georg Cantor's theory of infinite sets.’
      • ‘Goldbach also studied infinite sums, the theory of curves and the theory of equations.’
      • ‘This restriction makes the subject very different from the knot theory traditionally studied by mathematicians.’
      • ‘In particular he strongly criticised Cantor's and Dedekind's theories of irrational numbers.’
      • ‘His mathematical work covered Cartesian geometry and the theory of equations.’
      • ‘However he made many contributions to number theory and to the theory of equations.’

Phrases

  • in theory

    • Used in describing what is supposed to happen or be possible, usually with the implication that it does not in fact happen.

      ‘in theory, things can only get better; in practice, they may well become a lot worse’
      • ‘Working on Saturdays is always confusing because we start earlier and, in theory, end earlier.’
      • ‘In theory it may seem like a great idea but, in theory, so do so many ideas until they are put into practice.’
      • ‘The Freedom of Information Act is, in theory, a way of ensuring that happens.’
      • ‘Radar also uses microwaves, so that in theory it would be possible to cook food by putting it at the focus of a radar dish.’
      • ‘While in theory that's an admirable trait, in practice it's pretty uncomfortable.’
      • ‘This concept, though brilliant in theory, is utterly, utterly painful in practice.’
      • ‘However, although this sounds good in theory, in practice it never quite seems to work that way.’
      • ‘The precautionary principle sounds good in theory, but in practice it is a nightmare.’
      • ‘The software makes it possible, in theory, to see and manage files on any storage system or server.’
      • ‘These are ideas which are beautiful in theory but limp and bedraggled in practice.’
      in principle, on paper, in the abstract, all things being equal, in an ideal world
      View synonyms

Origin

Late 16th century (denoting a mental scheme of something to be done): via late Latin from Greek theōria ‘contemplation, speculation’, from theōros ‘spectator’.

Pronunciation

theory

/ˈθɪri//ˈTHirē/