The basic notions of the theory of binding may be defined as in (5) and (6): (5) (i) α is X-bound by β if and only if α and β are coindexed, β c-commands α, and β is in an X-position; (ii) α is X-free if and only if it is not X-bound; (iii) α is locally bound by β if and only if α is X-bound by β, and if γ Y-binds α then either γ Y-binds β or γ = β; (iv) α is locally X-bound by β if and only if α is locally bound and X-bound by β; (6) α is a variable if and only if (i) α = [NP e]; (ii) α is in an A-position (hence bears an A-GF); (iii) there is a β that locally Ᾱ-binds α. Cases (i) and (ii) of (5) define "bound" and "free" with "X" replaced by "A" or "Ᾱ".
- Chomsky (1993), a pag.184-185