As Peters points out in this and other work, the treatment of filler syllables continues to be problematic. To the extent that theoretical linguistic approaches to language acquisition have addressed the problem of morphology at all, this has been almost entirely in the domain of syntax. Thus, the phonological and prosodic characteristics of filler syllables in children's early speech have been largely ignored, the assumption being that the appearance of grammatical morphemes is ‘triggered’ by the maturation of syntactic representations (e.g. Radford, 1990). If this were the case, we would not expect to find crosslinguistic differences in the timing of the acquisition of determiners (Lleó & Demuth, 1999), nor the variable appearance of grammatical morphemes in some contexts and not others (Demuth, 1994, Gerken, 1996). These cases of crosslinguistic and within-language variation call for a more comprehensive account of early morpheme acquisition which can explain their variable presence or absence.