Grammatical relations have always constituted a primary focus of attention in the study of language. Within the last three decades, the topicality of this trend has increasingly been determined by the quest for a universal characterization of the language faculty which has shaped the goals and directives of most current works in theoretical linguistics. Although the realization patterns and syntactic functionality of grammatical relations are subject to cross-linguistic variation, studies in comparative grammar have provided suggestive evidence that the range of variation found can often be contained within the limits fixed by a discrete set of parameters. The investigation of these parameters has broached the possibility of a universal specification of the nature of grammatical relations. This thesis proposes that such a specification should be achieved by establishing regularities in the syntax-semantics interface within a constraint-based approach to linguistic analysis that integrates a precise computational interpretation. In keeping with this objective, a unification-based categorial grammar framework is developed which incorporates the semantic insights of a Neo-Davidsonian approach to verb semantics and predicate-argument combination, where thematic roles are defined as clusters of entailments of verb meanings. This framework is extended with an integrated approach to argument selection and selection change. Properties of the resulting system are demonstrated with respect to a variety of natural language phenomena concerning grammatical function changing, unaccusativity and clitic dislocation.