The particle ἄν (Hom. κέν, κέ) limits the meaning of the moods. It has two distinct uses:
a. In independent clauses: with the past tenses of the indicative and with the optative; also with the infinitive and participle representing the indicative or optative.
b. In dependent clauses: with the subjunctive.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].