Filler syllables: what is their status in emerging grammar?

Although it has long been observed that some children incorporate unglossab le syllables into their early utterances, it has been difficult to integrat e these 'fillers' into theories of language acquisition. Because they strad dle boundaries between phonology and morphosyntax, and between pragmatics a nd lexicon, they do not fit neatly into linguists' notions about 'modules' of language. Fillers have been reported in quite an array of languages, and yet they seem to be more common among learners of some languages than othe rs. Even when language is held constant, children seem to vary immensely as to whether they produce fillers at all. With more researchers reporting fi llers in more languages, it seems time to (1) review what we now know about fillers; (2) propose a reasonably unified set of criteria for identifying them; and (3) suggest an approach that will promote their further study.