A linguistic expression whose formation becomes subject to rules of the language system is grammaticalized. Speakers and hearers select and combine linguistic signs, including constructions and construction schemata, with diverse degrees of freedom. Constraints on this freedom imply the entrenchment of signs in the system of the language. Grammaticalization is the subjection of a linguistic construction or construction schema or of a linguistic operation to rules of grammar. Typically, a pivotal component of the construction is thereby converted into a grammatical formative, which is also said to be grammaticalized.
Early conceptions of grammaticalization were item-centered in the sense that a lexeme was said to be grammaticalized to a grammatical formative; for instance the English full verb have ‘possess’ was grammaticalized to a perfect auxiliary. In subsequent decades, more emphasis was laid on the fact that a grammatical formative functions in a grammatical construction, so the entire construction is grammaticalized. In the case of the example, this means that a periphrasis like [ have [Xed]V ]V becomes a member of the conjugation paradigm of X.
The term ‘grammaticalization theory’ has been used repeatedly in the literature. Critics of research in grammaticalization have reacted to this by denying the products of such research the status of a theory. As long as the criteria which allow us to distinguish between theories and other scientific products are not spelled out, this is a dispute over words. At any rate, a framework of concepts which have proved fruitful in research on grammatical variation and change has evolved by research in grammaticalization; and it is worth the effort to form it into a consistent conception. Section 2 of this website is devoted to this task.
The term grammaticalization was coined, in its French version grammaticalisation, in Meillet 1912, to designate a process in which something becomes grammatical. Some authors prefer the shorter variant grammaticization. It may have the advantage of excluding that meaning of grammatical in which it contrasts with ungrammatical. Instead, the counterpart of grammatical in the sense which underlies the abstract noun grammaticalization is ‘not subject to rules of grammar’.