This paper explores the question how far “letters” as one specific text type can be subdivided into smaller groups of texts (i.e. subtypes such as “requests”, “orders”, or “reports”) on the basis of socio-psychological and pragmatic dimensions and factors, including speech act and accommodation theory. This paper argues that this differentiation into socio-pragmatic subtypes actually can be made and that these subtypes materialize in significant systematic morphosyntactic variability. The idea is explored and illustrated on the basis of pronoun and relativizer variation in the late Middle English Paston Letters. In particular, it is shown how authors use their individual stylistic freedom to pursue specific communicative purposes in different types of letters.