Introduction : the nature of grammatical categories and their representation -- Philosophical background. Categories / Aristotle ; Concepts / Gottlob Frege ; Vagueness / Bertrand Russell ; Family resemblances / Ludwig Wittgenstein ; The phenomena of vagueness / Rosanna Keefe -- Categories in cognition. The boundaries of words and their meanings / William Labov ; Principles of categorization / Eleanor Rosch ; Categorization, fuzziness, and family resemblances / Ray Jackendoff ; Discreteness / Ronald W. Langacker ; The importance of categorization / George Lakoff -- Categories in grammar. Parts of speech / Otto Jespersen ; English word classes / David Crystal ; A notional approach to the parts of speech / John Lyons ; Syntactic categories and notional features / John M. Anderson ; Bounded regions / Ronald W. Langacker ; The discourse basis for lexical categories in universal grammar / Paul J. Hopper and Sandra A. Thompson ; Grammatical categories / John Taylor -- Gradience in grammar. Gradience / Dwight Bolinger ; Degrees of grammaticalness / Noam Chomsky ; Descriptive statement and serial relationship / Randolph Quirk ; On the analysis of linguistic vagueness / Jir̆í V. Neustupný ; Nouniness / John Robert Ross ; The coordination-subordination gradient / Randolph Quirk ... [et al.] ; The nature of graded judgments / Carson T. Schütze -- Criticisms and responses. Description of language design / Martin Joos ; 'Prototypes save' / Anna Wierzbicka ; Fuzziness and categorization / Denis Bouchard ; The discrete nature of syntactic categories : against a prototype-based account / Frederick J. Newmeyer.