A usage-based theory of language change developed by William Croft. This theory views language use as the interface that mediates between the conventions of a language (those aspects of use that make a language stable) and mechanisms that result in deviation from convention resulting in language change. For linguistic conventions to change someone must break a convention and this innovation must then undergo propagation : the change spreads through the linguistic community and becomes established as a new convention. Language change is viewed as a consequence of selectional pressures exerted on linguistic conventions, because language is a system in use that changes as a response to the new uses to which it is put. Borrowing ideas from evolutionary theory Croft argues that innovations which are successful, in the sense of being selected by language users by virtue of being replicated, give rise to propagation and thus result in language change.

As this theory subscribes to the usage-based thesis, the key construct in the theory of utterance selection is the utterance. The elements of an utterance that are reproduced by language users are referred to as replicators.

The elements of language that are realized in an utterance and that can therefore count as replicators include words, morphemes and grammatical constructions.

Croft calls these linguistic replicators lingueme s.