 that the two basic constituents of a sentence - the noun phrase (NP) and the verb phrase (VP) - are associated with the logical/grammatical functions of subject and predicate (cf.phrase structure rules and sentence).In fact, copular sentences that maintain the canonical groupings are not adequate on empirical grounds, since a very unorthodox left-branching structure is necessary, or if one rejects the canonical groupings and positions the subject inside a VP-like constituent, then one has to assume that the subject NP and copula verb can form a type of VP to the exclusion of the predicative expression.