The author analyzes, from a historical sociolinguistic point of view, selected domains of morphosyntactic variation in a 250,000 word collection of the Middle English Paston Letters (1421-1503). In three case studies, two nominal and one verbal variable are described and discussed in detail: the replacement of Old English pronouns by borrowed pronouns, the introduction and spread of >wh-relativizers, and the spread and routinization of light verb constructions (take, make, give, have, do plus deverbal noun). While the author aims at a balanced integration of different approaches in sociolinguistics, cognitive linguistics, typology, and language change, the main focus is on social network theory and the role of the linguistic individual in the formation and change of linguistic structures.