Studies of phonological assimilation have played a central role in the development of current phonological theory. As widely discussed in the literature, assimilation is an extremely common phonological process cross-linguistically and therefore an adequate phonological theory should represent it simply and naturally. This has led to the current view of assimilation as spreading (Clements 1976; Goldsmith 1976; Hayes 1986; among others). Much less work has addressed itself to the issue of dissimilation, but recently it has been suggested that dissimilation should be analysed as delinking followed by default fill-in (Odden 1987; Poser 1987; McCarthy 1988; Yip 1988).