A grammar that generates simple Phrase-markers [...] may be based on a vocabulary of symbols that includes both 'formatives' ('the', 'boy', etc.) and 'category symbols' (S, NP, V, etc.). The formatives, furthermore, can be subdivided into 'lexical' items ('sincerity', 'boy') and 'grammatical' items ('Perfect', 'Possessive', etc.[...]). - Chomsky (1969), a pag.65