[…] the term "pronominal" is purely descriptive; it does not refer to a feature, apart from the grammatical features person, number, gender.
- Chomsky (1993), a pag.61

A pronominal has no grammatical features other than φ-features, and may or may not have a phonological matrix. Specifically, we have the definition (11) [...] α is a "pronominal" if and only if α = [NP F, (P)], where P is a phonological matrix and F ⊂ ø, and either (i) or (ii): (i) α is free; (ii) α is locally A-bound by β with an independent θ-role. If α = [NP F], it is PRO; otherwise, α is a pronoun.
- Chomsky (1993), a pag.330