Herbert Weir Smyth, A Greek Grammar for Colleges

a. The present unreal condition with εἰ with the optative in the protasis and ἄν with the optative in the apodosis (in form like a less vivid future condition in Attic) is very rare (Ψ 274). In B 80, Ω 220 we have a combination of a past protasis (imperfect or aorist indicative) with present apodosis (with κέν and the optative).

b. Past unreal conditions have, in the protasis, the imperfect or aorist indicative; in the apodosis, either the imperfect or aorist indicative with ἄν or κέ or the aorist or present optative with κέ. Thus, καί νύ κεν ἔνθ᾽ ἀπόλοιτο . . . Αἰνεία_ς, εἰ μὴ ἄρ᾽ ὀξὺ νόησε . . . Ἀφροδί_τη and here Aeneas had perished, if Aphrodite had not quickly observed him E 311.