A discussion of constraints on ellipsis after auxiliaries in English focuses on a particular analytic problem concerning nonfinite verb phrases using "be", which has a historical dimension. A solution involving the morphological claim about the copula and its incorporation of tense-distinctions is proposed and discussed in the context of Generalized Phrase Structure Grammar (GPSG). It is concluded that there is a synchronic and diachronic justification for a GPSG analysis of the tensed forms of the English copula as distinct from nonauxiliary verbs in two respects: (1) the semantics of their combination with tense is given lexically, and (2) they lack the morphology of verbal inflection. Advantages found in this analysis are that the copula is consistent with the behavior of the auxiliary "have" and that it deals naturally with the loss of the ellipsis construction with tensed antecedent found in earlier English. (MSE)