Sentence stress is not always a sufficient condition for interpretation as focus. An insightful analysis of the appropriate generalizations can be accommodated under a 'modular' approach to grammatical theory. Certain observations concerning the stress properties of WH questions are shown to be consistent with the assumptions of trace theory as developed in, e.g., Chomsky & Lasnik 1977, where the relationship between focus and stress is mediated by S-structure. The notion of focus has no consistent pragmatic characterization; it is, rather, a grammatical notion. The interpretation of this grammatical notion in particular discourse contexts is provided by rules of Discourse Grammar using the predicate 'c-construable', which is here defined.