Crosslinguistic Study as a Method in Developmental Psycholinguistics, Null Hypothesis: Developmental Universals, Conceptual Development and the Construction of Grammar, Formal Pattern Preferences and Grammar, Concepts are Combined in Grammatical Morphemes According to Semantic Affinities in Grammatical Morphemes are Positioned According to Their Scope of Operation, Grammatical Markers are placed According to Principles of Semantic Relevance, Morphological Systems are Constructed According to Formal (Non-semantic) Criteria, Hypotheses of Specific Language Effects, Form-Function Interaction Influences Rate or Sequence of Development, Particular Linguistic Forms are Relatively More Accessible, Holding Content Constant, Separate Marking of Notions in Particular Languages Reveals a Conceptual Substratum, Language-specific Co-occurrences Reveal Patterns of Conceptual Relavance, Crosslinguistic Differences in Degree of Coding an Area Reveal Linguistic Capacities, The Plan of the Book. The Acquisition of Japanese Introduction Grammatical Sketch of Japanese, Sources of Evidence, Overall Course of Development, The Data, Typical Errors, Error-Free Acquisitions, Timing of Acquisition, Reorganizations in Development, The Setting of Language Acquisition, Cognitive Pacesetting of Linguistic Development, Linguistic Pacesetting of Cognitive Development, Individual Differences, Input and Adult-Child Interactions, Conclusions.