Initially, two additional levels of representation were introduced (LF — Logical Form, and PF — Phonetic Form), but in the 1970s, Chomsky sketched out a new program of research known as Minimalism, in which Deep Structure and Surface Structure are no longer featured and PF and LF remain as the only levels of representation.
Nun principio, introducíronse dous niveis adicionais de representación: a Forma Lóxica (LF) e a Forma Fonética (PF); posteriormente, nos anos noventa, Chomsky presentou un novo programa de estudo coñecido como minimalismo (ver máis abaixo), no cal a Estrutura Profunda e a Estrutura Superficial xa non encaixaban, mentres que PF e LF permaneceron como os únicos niveis de representación.