Abstract.This paper will discuss an alteration in the phonological components of Alemannic and Bavarian within the framework of generative phonology. First, an apparent discrepancy in the earliest documents concerning the relative chronology of two early rules will be accounted for. The rules are the second sound shift and the rule loweringautoao. Internal evidence will also be presented for the diphthongal status of the orthographic symbolao(and likewiseae). Second, the changes discussed here represent further evidence for the simplification principle recently discussed by Kiparsky. It is important to note that documented examples of simplification of synchronically existing rules are empirical evidence for the generative model of natural language.