RT Journal Article SR Electronic(1) A1 Hartman Keiser, Steven YR 2009 T1 When ‘Speech Islands’ Aren’t Islands: Parallel independent development, drift, and minimal levels of contact for diffusion JF Diachronica VO 26 IS 1 SP 1 OP 35 DO https://doi.org/10.1075/dia.26.1.01kei PB John Benjamins SN 0176-4225, AB 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)., UL https://www.jbe-platform.com/content/journals/10.1075/dia.26.1.01kei