1. Hume D (1739/1978) A Treatise of Human Nature (Clarendon, Oxford).
2. Quine WVO (1960) Word and Object (MIT Press, Cambridge, MA).
3. Goodman N (1955) Fact, Fiction, and Forecast (Harvard Univ Press, Cambridge, MA).
4. Markman E (1989) Categorization and Naming in Children (MIT Press, Cambridge, MA).