Generative linguists and categorial grammarians aim to develop a system of Universal Grammar to explain structural variation across languages while at the same time accounting for uniformity in interpretation. The generative tradition has provided a broad empirical perspective on cross-linguistic diversity. The type-logical tradition provides logical tools to understand this diversity in deductive terms. This dissertation aims to establish a two-way communication between these two perspectives.

This book presents the logic of variation as a system of universal grammar. Its central claim is that the combination of structural variation and uniform semantic interpretation in wh-question formation can be accounted for in terms of three assumptions: (1) Higher-order type assignment: higher-order type assignment to wh-elements accounts for the uniformity in the semantic interpretation of wh-questions; (2) A fixed structural module: variation in the structural realization is bounded by a restricted set of structural rules which is claimed to be fixed by Universal Grammar; consequently, (3) Strong lexicalism: cross-linguistic variation in wh-question formation must be entirely reducible to differences in lexical type-assignment, that is, there are no language-specific structural rules. Empirical support for this view is provided for by presenting a broad cross-linguistic analysis of languages that structurally differ in wh-question formation.

This study will be relevant to linguists in the generative tradition and mathematical linguists who are concerned with the formal system of natural language variation and the syntax-semantics interface. The various grammar fragments discussed in the thesis have been implemented with Grail, Richard Moot's parser for categorial type logics. The CD-rom accompanying this thesis allows the reader to further explore the fragments which are discussed and/or to formulate alternative analyses.