Let us refer to a position in LF to which a θ-role is assigned as a "θ-position". Idioms apart, each position satisfying the subcategorization features of the lexical head of a construction is a θ-position; in the terminology of X-bar theory, each complement position is a θ-position [...] Some θ-positions are filled by arguments; all complements of a head are θ-positions apart from examples restructured by idiom rules in ways to which we will return; the subject is a θ-position where a θ-role is determined for it.
- Chomsky (1993), a pag.35-36