The ordinary uses of the moods in relative clauses are as follows:
a. The present and past tenses of the indicative without ἄν express a fact or the assumption of a fact. The future indicative is used to denote purpose, present intention, or an intended result.
b. The indicative with ἄν denotes unreality.
c. The subjunctive with ἄν expresses a possible or supposed fact in future time or a generality in present time. The subjunctive without ἄν is used in indirect questions ( cross1805 b).
d. The optative without ἄν expresses a wish, a possibility less distinctly conceived, or a generality in past time.
e. The optative with ἄν is potential, and is used either in conditional relative clauses with an optative in the main clause, or alone, as
μἴ ἔστιν ἐλπίς, ᾗ μόνῃ σωθεῖμεν ἄν
g. The infinitive occurs in relative clauses in indirect discourse ( cross2631).
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].