Methodological reflections on the emergence of Old Frisian

The question addressed in this article is whether it is possible to identify the time of the emergence of Frisian from the rest of West Germanic. Some of the criteria used in determining the chronology of Frisian language history are evaluated in terms of their temporal and spatial aspects. Phonological features that appear to differentiate languages from a present-day perspective disappear in a haze of synchronic and diatopic allophonic alternations. Reconstructions of the order of phonological developments often turn out to be best-fit interpretations of changes whose precise character, age and location are hard to determine. Besides, reconstructions of regional distribution are obscured by subsequent migrations and dialect shifts. Consequently, the splits in a language family tree are not bifurcations, but bushes of variation, where only hindsight allows an identification of the chronology and the decisive factors involved.