In historical linguistics, grammaticalization (also known as grammatization or grammaticization) is a process of language change by which words representing objects and actions (i.e. nouns and verbs) become grammatical markers (such as affixes or prepositions). Thus it creates new function words from content words, rather than deriving them from existing bound, inflectional constructions. For example, the Old English verb willan 'to want', 'to wish' has become the Modern English auxiliary verb will, which expresses intention or simply futurity. Some concepts are often grammaticalized, while others, such as evidentiality, are not so much.[1]
For an understanding of this process, a distinction needs to be made between lexical items or content words, which carry specific lexical meaning, and grammatical items or function words, which serve mainly to express grammatical relationships between the different words in an utterance. Grammaticalization has been defined as "the change whereby lexical items and constructions come in certain linguistic contexts to serve grammatical functions, and, once grammaticalized, continue to develop new grammatical functions".[2] Where grammaticalization takes place, nouns and verbs which carry certain lexical meaning develop over time into grammatical items such as auxiliaries, case markers, inflections, and sentence connectives.
A well-known example of grammaticalization is that of the process in which the lexical cluster let us, for example in "let us eat", is reduced to let's as in "let's you and me fight". Here, the phrase has lost its lexical meaning of "allow us" and has become an auxiliary introducing a suggestion, the pronoun 'us' reduced first to a suffix and then to an unanalyzed phoneme.
In other areas of linguistics, the term grammaticalization has taken on a much broader meaning. These other senses of the term are discussed below.