This paper addresses the analysis of English ing-clauses and discusses its theoretical significance with respect to the architecture of grammatical categories. English ing-clauses pose two major descriptive issues: first, whether the two historically distinct clause-types of gerunds and participles can be collapsed into a single category, and second, whether ing-clauses still relate to their phrasal origins as (historical) noun phrases and adjectival/adverbial phrases. It is argued that neither question can receive a straightforward answer, as the existing evidence is simply contradictory. This, in turn, has theoretical consequences. English ing-clauses show that language users can operate with different grammatical generalizations at once. The representation of grammatical categories must therefore be internally complex, allowing grammatical categories to be simultaneously unified and distinct, interrelated and autonomous.