When ‘Speech Islands’ Aren’t Islands: Parallel independent development, drift, and minimal levels of contact for diffusion

This study explores the related concepts of parallel independent development and drift, highlighting in particular the challenge of quantifying isolation. I analyze the precisely synchronized spread of a sound change, the monophthongization of /aɪ/, across Pennsylvania German ‘speech islands’ in the American Midwest. A key finding is that the intensity and duration of interspeaker contact required to catalyze apparent parallel developments may have lower than expected thresholds. The significance of extensive yet low-intensity cross-migration patterns across these communities at particular points in their histories ultimately leads to an exploration of the minimal level of contact required for diffusion of a change and feeds into recent discussion on the social contexts for transmission and diffusion (e.g., Labov 2007).