The process of apocope in Medieval Spanish offers a glimpse into the interaction of structural and sociological constraints on linguistic behavior. Of the word final unstressed vowels /e/, /o/ and /a/, the twelfth and thirteenth century Spanish /e/, and less often /o/ were effaced exposing new consonants and consonant clusters. Written documentation of the period clearly indicates the loss of the vowel in environments where Modern Spanish has sustained the loss and in others where it has not, cf. Latin panem > Old Spanish pan, Modern Spanish pan. and Latin noctem > Old Spanish noch (in texts), Modern Spanish noche. By the fifteenth century, apocoped vowels were restored except after dental consonants, i.e., /l, r, s, n, ć (>θ), d/. The loss and subsequent restoration of these vowels appears to reflect syntagmatic, sociological and paradigmatic aspects of language function. To what extent can these factors be isolated, and their relative influence examined?