Yarden Kedar, Marianella Casasola and Barbara Lust

Does the lexicon alone determine reference or does syntactic phrase structure contribute to this process as well? Researchers have proposed contrasting responses to this question. Some take young children’s frequent omissions of functional categories as evidence for diminished syntactic knowledge, arguing instead that children rely primarily on lexical categories in the early stages of language acquisition (e.g., Radford 1990, 1997, Tomasello 2000a, 2000b, 2002, Tsimpli, 1991). In contrast, others argue for early access to functional categories, even when these are absent in children’s speech (Boser, Lust, Santelmann, & Whitman 1992, Demuth 1994, Gerken & McIntosh 1993, Hyams 1992, Lust 1994, Poeppel & Wexler 1993, Weissenborn 1990). These debates are important to learning theories, which point to exposure and statistical frequency, and to current linguistic theory, which defines functional categories as the heads of their own projections (Abney 1987, Chomsky 1995), hence granting them a central role in the language faculty. Functional categories include grammatical elements such as determiners, complementizers and inflections, which are realized in language by function words (e.g., the, and) and morphemes (e.g., -ed, -s). This category stands in contrast to lexical categories (nouns, verbs, adverbs and adjectives), which are realized in language by content words, that is, words that convey meaning (e.g., ball, beauty). Although function words are highly frequent in language, and have been proposed to be important cues for detecting morphological, phrasal and sentential structure (Clark & Clark 1977, Gerken, Landau, & Remez 1990, Gerken & McIntosh 1993, Maratsos 1982, Shi, Morgan & Allopenna 1998), young children have been consistently reported to omit function words from their speech at early stages of productive language (Bloom 1970, Bowerman 1973, Braine 1976, Brown 1973, Brown & Bellugi, 1964). Accordingly, several researchers assume that young ‘telegraphic speakers’ are not aware of function words as distinct units with a syntactic and semantic role. Instead, children in the early stages of language development are argued to rely on lexical categories represented by content words such as nouns and verbs for inferring meaning and reference in other speakers’ speech (Bowerman 1973, Brown 1973, Macnamara 1982, Pinker 1982, 1984, Schlesinger 1971, 1981, Tomasello 2000a, 2000b, 2002). This view, however, has been challenged by evidence that young children are sensitive to function words in perception, despite omitting them from their productive speech (Gelman & Taylor 1984, Gerken et al. 1990, Katz, Baker, & Macnamara 1974, Petretic & Tweney 1977, Shady 1996, Shady, Jusczyk, & Gerken 1998, Shipley, Smith, & Gleitman 1969). These findings support the claim that young children and even newborns (Shi, Werker, & Morgan 1999) are, in fact, able to distinguish between function words versus content or nonsense words, based on a constellation of perceptual and distributional cues. Based on this evidence, it seems that children’s omission of function words is not the outcome of a deficit in linguistic competence, but rather, as Gerken and colleagues have suggested, the result of motor constraints on the alteration between weakly and strongly stressed syllables in speech production at early stages of language acquisition (Gerken et al. 1990, Gerken & McIntosh 1993, Gerken 1996, Boyle & Gerken 1997). One remaining question is whether young children can not only detect function words in the speech stream, but also whether they can distinguish between function words which carry