This book focuses on the nature and development of knowledge concerning grammar and the meanings coded by grammar. This knowledge is inferred from performance, from sentences and the settings in which they are spoken, and from signs of comprehension or incomprehension of sentences by preschool children. The first two stages of linguistic development are discussed. Stage 1 is the threshold of syntax, when children begin to combine words to make sentences which are always limited to the same small set of semantic relations, including nomination, recurrence, disappearance, attribution, possession, and agency. Stage 2 is concerned with the modulations of basic structural meanings--modulations for number, time, aspect, specificity--through the gradual acquisition of grammatical morphemes such as inflections, prepositions, articles, and case markers. Fourteen morphemes are studied and it is shown that the order of their acquisition is almost identical across children and is predicted by their relative semantic and grammatical complexity. (LL)