Auxiliation is the diachronic process of creating an auxiliary verb from a full verb.
The change from the Old English full verb willan 'want' to a future auxiliary (as in She will go) is an example of auxiliation.
According to Kuteva (2001:1), the term was coined by Benveniste (1968).
- Benveniste, Émile. 1968. "Mutations of linguistic categories." In: Lehmann, Winfred P. & Malkiel, Yakov (eds.) Directions for historical linguistics: A symposium. Austin: University of Texas Press, 85-94.
- Kuteva, Tania. 2001. Auxiliation: An enquiry into the nature of grammaticalization. Oxford: Oxford University Press.