Frontmatter -- Preface -- Contents -- Figures -- Tables -- 1. Introduction -- 2. The Phenomena -- 3. Developing a Theory -- 4. Empirical Evaluation -- 5. Other Psychological Research -- 6. Origins of Ontologica! Knowledge -- 7. Follow-up Studies -- 8. Other Developmental Research -- 9. A Closer Look at the Theory -- 10. Constraints and Development -- Appendixes. References. Index -- Appendix A. Sommers' Proof of the Law of Categorical Inclusion -- Appendix Β. Generating an M-Constrained Matrix from Random Data -- Appendix C. Three Grade-School Studies -- References -- Author Index -- Subject Index