[…] assume UG to have three fundamental components [...] The rules of the syntax generate S-structures. One system of interpretive rules, those of the PF component, associates S-structures with representations in phonetic form (PF); another system, the rules of the LF-component, associates S-structure with representations in "logical form" (LF), where it is understood that the properties of LF are to be determined empirically and not by some extrinsic concern such as the task of determining ontological commitment of formalizing inference [...] At the most general level of description, the goal of a grammar is to express the association between representations of form and representations of meaning.
- Chomsky (1993), a pag.17

[…] several theories have been proposed that are fairly intricate in their internal structure, so that when a small change is introduced there are often consequences throughout this range of phenomena, not to speak of others. This property of the theories I will investigate is a desirable one; there is good reason to suppose that the correct theory of universal grammar in the sense of this discussion (henceforth: UG) will be of this sort.
- Chomsky (1993), a pag.3