[…] let us assume a variant based on two categories of traditional grammar: substantive ([+N]), including nouns and adjectives, and predicate ([+V]), including verbs and adjectives. Let us refer to substantives and predicates as the "lexical categories". - Chomsky (1993), a pag.48
[…] if α is not an empty category, call it a "lexical category". - Chomsky (1993), a pag.330