General English

  • noun an explanation of something which has not been proved but which you believe is true
  • noun a careful scientific explanation of why something happens
  • noun a statement of general principles which may not apply in practice

General Science

  • noun a possible explanation of how or why something happens which has not been confirmed by experimental evidence


  • noun a system of ideas or principles explaining something


  • noun a statement of the general principle of how something should work


  • A set of statements, concepts, principles, and/or rules whose intention is to explain and/or predict phenomena using logical and scientific arguments. Examples include quantum theory, the Bardeen-Cooper-Schrieffer theory, and the Grand Unified Theory.
  • A branch of science in which a theory (1) is applied, as opposed to practice. Examples include circuit theory, and information theory.


  • noun an argument which explains a scientific fact

Origin & History of “theory”

The etymological notion underlying theory is of ‘looking’; only secondarily did it develop via ‘contemplation’ to ‘mental conception’. It comes via late Latin theōria from Greek theōríā ‘contemplation, speculation, theory’. this was a derivative of theōrós ‘spectator’, which was formed from the base thea- (source also of theā́sthai ‘watch, look at’, from which English gets theatre). Also derived from theōrós was theōreī́n ‘look at’, which formed the basis of theṓrēma ‘speculation, intuition, theory’, acquired by English via late Latin theōrēma as theorem (16th c.). From the same source comes theoretical (17th c.).