The complexities of the Welsh copula

The Welsh copula has a complex set of forms reflecting agreement, tense, polarity, the distinction between main and complement clauses, the presence of a gap as subject or complement, and the contrast between predicative and equative interpretations. An HPSG analysis of the full set of complexities is possible given a principle of blocking, whereby constraints with more specific antecedents take precedence over constraints with less specific antecedents, and a distinction between morphosyntactic features relevant to syntax and morphosyntactic features relevant to morphology.