Thus suppose that a grammar were to contain the rewriting rules (12) (i) S → Adverbial⁀NP⁀Aux⁀VP ('Naturally, John will leave'); (ii) S → NP⁀Aux⁀VP ('John will leave') [...] Then Subject-of is defined by both (i) and (ii), so that 'John' is Subject-of the sentences accompanying both (i) and (ii). - Chomsky (1969), a pag.72