Number fission from a formal and functional perspective

Abstract Modal verbs in German show phonologically unconditioned umlaut in the pres.pl versus pres.sg whose functional motivation is unclear. Based on a large sample of dialectological data, I explore the distribution of this umlaut as well as other irregularization strategies like contractions and/or consonant mutations in different paradigm cells. My observations point to the conclusion that these facets of irregularity are morphomic in that they serve no other function than signaling inflectional class coherence. A promising approach to capture these complex patterns of stem allomorphy is Information-based Morphology (IBM), an inferential-realizational approach to morphology developed in the context of Head-driven Phrase Structure Grammar (HPSG). The concept of a stem space allows for expressing implicational or directed generalizations in stem formation and their mapping to phonology. In diachronic terms, however, transcategorial number marking, as proposed in the relevant literature, is a plausible functional motivation for the analogical extension of umlaut as a verbal plural marker.