# Definition of "theory"

## theory

/ˈθɪə.ɹi/

### noun

*countable and uncountable*,*plural*theories(mathematics) A field of study attempting to exhaustively describe a particular class of constructs.

(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).

(obsolete) Mental conception; reflection, consideration.