The acquisition of connective forms and the meaning relations between connected clauses in the development of complex sentences is described for four children from two to three years of age. The major results of the study include the developmental interactions between syntactic connectives and meaning relations, and between these interactions and the discourse environments in which they occurred. The first syntactic connective the children learned, and, was the most general: semantically, and was used to encode conjunction with all of the different conjunction meaning relations in the order Additive < Temporal < Causal < Adversative. Other connectives were semantically more specific, and were learned subsequently with different syntactic structures in the order Conjunction < Complementation < Relativization. These results are discussed in terms of FORM, relative linguistic complexity; CONTENT, the intersection of form with conceptual and semantic factors affecting acquisition; and USE, discourse cohesion.

The discourse interaction between adult and child was examined in terms of the content of their utterances, and the linguistic and contextual relations between their messages, in order to investigate how children use the information from adults' input sentences to form contingent responses. The analyses described were based on longitudinal data from four children from approximately 21 to 3 6 months of age. Categories of child discourse, their development and their interactions with aspects of prior adult utterances form the major results of the study. Child utterances were identified as adjacent (immediately preceded by an adult utterance), or as nonadjacent (not immediately preceded by an adult utterance). Adjacent utterances were either contingent (shared the same topic and added new information relative to the topic of the prior utterance), imitative (shared the same topic but did not add new information), or noncontingent (did not share the same topic). From the beginning, adjacent speech was greater than nonadjacent speech. Contingent speech increased over time; in particular, linguistically contingent speech (that expanded the verb relation of the prior adult utterance with added or replaced constituents within a clause) showed the greatest developmental increase. Linguistically contingent speech occurred more often after questions than nonquestions. The results are discussed in terms of how the differential requirements for processing information in antecedent messages is related to language learning.

In order to explore the function of imitation for first language learning, imitative and spontaneous utterances were compared in the naturalistic speech of six children in the course of their development from single-word utterances (when mean length of utterance was essentially 1.0) to the emergence of grammar (when mean length of utterance approached 2.0). The relative extent of imitation and the lexical and the grammatical variation between imitative and spontaneous speech were determined. There were inter-subject differences in the extent of imitation, but each child was consistent in the tendency to imitate or not to imitate across time. For those children who imitated, there were both lexical and grammatical differences in imitative and spontaneous speech, and a developmental shift from imitative to spontaneous use of particular words and semantic-syntactic relations between words. The results are discussed as evidence of an active processing of model utterances relative to the contexts in which they occur for information for language learning.

Children's expressions of causality in natural discourse with adults were examined in terms of linguistic, contextual, and pragmatic influences. Specifically, the causal statements, questions, and responses to causal questions of eight 2-3-year-old children were examined in terms of developments in language content, form, and use. With respect to content, the referential and functional uses of causal expressions for both children and adults were to ongoing or imminent situations, with the speaker commenting on his or her intention to act, or requesting the listener to act. The major categories of reference in all three utterance types were negation, direction, and intention. In terms of form, there were (a) increasing use of connectives to link clauses for all the children, and (b) three main patterns of clause order differentiating among the children: cause/effect, effect/cause, and equal use of both orders. The use of expressions of causality developed in the order: child statements less than adult questions less than child responses less than child questions. The relationship of the linguistic context to these developments was found to be one of mutual influence between child and adult. The results are discussed in terms of previous hypotheses concerning (a) causal reasoning (especially those put forth by Piaget, and by Werner & Kaplan in 1963), (b) the relationship between language and conceptual development, (c) the constraints involved in different discourse situations, and (d) variation in child language.

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