The metrical basis for children's subjectless sentences

Young English speakers often omit sentential subjects but infrequently omit objects. In this paper I consider five accounts for these omissions that differ in the explanation of why children make omissions (grammar versus production constraints) and what causes the asymmetry in subject and object omissions. Hyams (1986, Language acquisition and the theory of parameters, Dordrecht, Reidel; 1987, Paper presented at the Boston University Conference on Language Development, October) proposes that children are born with an innate grammar that causes them to omit pronominal subjects. Valian (1989, Papers and Reports on Child Language Development, 28, 156-163) notes that subject deletion is acceptable in casual adult English: Based on these data, children omit subjects when sentence complexity puts too great a burden on the production system. On a pragmatic account (Bates, 1976, Language and context. New York: Academic Press; Greenfield & Smith, 1976, The structure of communication in early language development. New York: Academic Press), children have limited production abilities and omit the least communicatively informative elements: Because subjects typically contain given information, they are frequently omitted. P. Bloom (1989, Papers and Reports on Child Language Development, 28, 57-63) argues that processing considerations cause children to expand sentences rightward, at the expense of leftward elements. Finally, I propose a metrical hypothesis in which children omit weakly stressed syllables, including pronouns and other function morphemes, particularly from iambic (weak-strong) feet. Data from an imitation task strongly support the metrical hypothesis over the others. The results are examined in light of a model of developing speech production.