Let us formulate these observations as a guiding principle for the theory to be developed: (38) Representations at each syntactic level (i.e. LF, and D- and S-structure) are projected from the lexicon, in that they observe the subcategorization properties of lexical items. Let us call the principle and later refiniments the "projection principle" for syntactic representations.
- Chomsky (1993), Pag. 29

Consider structural configurations of the form (5), where α is an immediate constituent of γ: (5) (i) [γ...α...β...]; (ii) [γ...β...α...] [...] We can restate the projection principle [...] as (6): (6) (i) if β is an immediate constituent of γ in (5) at Li, and γ = ᾱ, then α -marks β in γ; (ii) if α selects β in γ as a lexical property, then α selects β in γ at Li; (iii) if α selects β in γ at Li, then α selects β in γ at Lj. The variables Li, Lj range over what we are considering throughout to be the "syntactic levels": LF, D-structure, S-structure.
- Chomsky (1993), Pag. 38