theory

Noun

theory (countable and uncountable, plural theories)

1. A description of an event or system that is considered to be accurate.
   • As they encrease the hatred of vice in some, so doe they enlarge the theory of wickednesse in all.1646, Thomas Browne, Pseudodoxia Epidemica, VII.19
2. 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.
   • In its most proper acceptation, theory means the completed result of philosophical induction from experience.1843, John Stuart Mill, ""A System of Logic, Ratiocinative and Inductive, ..., Bk V, Ch 7
   • Does this mean, then, that there can be no such thing as a theory of literature?1990, Tony Bennett, Outside Literature, page 139
3. (uncountable) The underlying principles or methods of a given technical skill, art etc., as opposed to its practice.
   • Lopukhov wrote a number of books and articles on ballet theory, as well as his memoirs.1998, Elizabeth Souritz, The Great History of Russian Ballet

   Antonyms:

   praxis

4. A field of study attempting to exhaustively describe a particular class of constructs.
   • Knot theory classifies the mappings of a circle into 3-space.
   • 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?1999, Wes DeMott, Vapors
5. (countable) 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.
6. (chess and similar games) The standardization and study of fixed sequences of moves, especially in the opening phase of a game.
   • Near-synonym: joseki

   Synonyms:

   joseki

7. (obsolete) Mental conception; reflection, consideration.
8. (informal) A hypothesis or conjecture.