Model theory is the study of the interpretation of any language, formal or natural, by means of set-theoretic structures.[1] Its primary branch is a field of mathematics, sometimes referred to as first-order model theory.[2]
Typically, model theory begins by specifying a list of symbols and rules for forming sentences from these symbols. An assembly of such sentences and their evaluation as true or false constitutes a model. Thus, a sentence p might be assigned the value true in model M, and M is said to be a model of p. It is said that M is a model of a set of sentences if and only if M is a model of each sentence in the set.[3]
Classical model theory proves various propositions about models, an example being "there is no set of sentences whose models constitute all possible finite models". A great deal of model theory consists of finding ways to construct models that enable proofs of various theorems.[3]