Definition of theory noun from the Oxford Advanced Learner's Dictionary

        

    theory

     noun
    noun
    BrE BrE//ˈθɪəri//
     
    ; NAmE NAmE//ˈθɪri//
     
    , NAmE//ˈθiːəri//
     
    (pl. theories) Experiments and research
     
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  1. 1  [countable, uncountable] a formal set of ideas that is intended to explain why something happens or exists According to the theory of relativity, nothing can travel faster than light. The debate is centred around two conflicting theories. CollocationsScientific researchTheory formulate/​advance a theory/​hypothesis build/​construct/​create/​develop a simple/​theoretical/​mathematical model develop/​establish/​provide/​use a theoretical/​conceptual framework advance/​argue/​develop the thesis that… explore an idea/​a concept/​a hypothesis make a prediction/​an inference base a prediction/​your calculations on something investigate/​evaluate/​accept/​challenge/​reject a theory/​hypothesis/​modelExperiment design an experiment/​a questionnaire/​a study/​a test do research/​an experiment/​an analysis make observations/​measurements/​calculations carry out/​conduct/​perform an experiment/​a test/​a longitudinal study/​observations/​clinical trials run an experiment/​a simulation/​clinical trials repeat an experiment/​a test/​an analysis replicate a study/​the results/​the findings observe/​study/​examine/​investigate/​assess a pattern/​a process/​a behaviour/(especially US English) a behavior fund/​support the research/​project/​study seek/​provide/​get/​secure funding for researchResults collect/​gather/​extract data/​information yield data/​evidence/​similar findings/​the same results analyse/​examine the data/​soil samples/​a specimen consider/​compare/​interpret the results/​findings fit the data/​model confirm/​support/​verify a prediction/​a hypothesis/​the results/​the findings prove a conjecture/​hypothesis/​theorem draw/​make/​reach the same conclusions read/​review the records/​literature describe/​report an experiment/​a study present/​publish/​summarize the results/​findings present/​publish/​read/​review/​cite a paper in a scientific journal See related entries: Experiments and research
  2. 2  [uncountable] the principles on which a particular subject is based the theory and practice of language teaching literary theory
  3. 3  [countable] theory (that…) an opinion or idea that somebody believes is true but that is not proved I have this theory that most people prefer being at work to being at home.
  4. Word Origin late 16th cent. (denoting a mental scheme of something to be done): via late Latin from Greek theōria ‘contemplation, speculation’, from theōros ‘spectator’.Extra examples Current feminist theory consists of several different trends. Each school has its own set of theories. Einstein’s general theory of relativity He has a theory about why dogs walk in circles before going to sleep. His comments are just abstract theory and show little understanding of the realities of the situation. In theory, these machines should last for ten years. Keynes misinterpreted the classical theory of interest. One of her pet theories is that people who restrict their calorie intake live longer. Police are working on the theory that the murderer was known to the family. a conspiracy theory about the princess’s death a grand unified theory of the physical forces governing matter the distinction/​relationship between theory and practice the dominant strand of postmodern theory the existence of a grand unified theory that determines everything in the universe According to Einstein’s theory of relativity, nothing can travel faster than light. Further experiments seemed to confirm this theory. He wrote a number of books on political theory. If the theory is correct, any child can be taught to be a musical genius. In theory, all children get an equal chance at school. It is a theory that cannot be proved or disproved. Marx’s theories of history raise one or two major questions. She doesn’t agree with the theory that rich people work harder than poor people. The theory was first advanced back in the 16th century. There are conflicting theories as to the very early origins of mankind. This is all theory so far…you’ll need to back it up with facts. You can neither prove nor disprove this theory. You will have to study both the theory and practice of education.Idioms  used to say that a particular statement is supposed to be true but may in fact be wrong In theory, these machines should last for ten years or more. That sounds fine in theory, but have you really thought it through? ‘Aren’t you supposed to be retired?’ ‘Yes, in theory.’
See the Oxford Advanced American Dictionary entry: theory