Georg Autenrieth, A Homeric Dictionary

εἰ : if, if only, whether; conjunction used in the expression of a wish or a condition, and in indirect questions.— I. As particle of wishing, εἰ or εἰ γάρ, would that, O that, is foll. by the optative.—II. Interrogatively, whether, foll. by such construction as the meaning requires, e. g., κατάλεξον | εἰ καὶ Λα_έρτῃ αὐτὴν ὁδὸν ἄγγελος ἔλθω, ‘am to go,’ Od. 16.138.—III. In conditional clauses εἰ (εἰ μή), and with the subj. often (sometimes w. the opt.) εἴ κεν, rarely w. ἄν, εἰ δ᾽ ἂν ἐμοὶ τι_μὴν Πρίαμος Πριάμοιό τε παῖδες | τι?νειν οὐκ ἐθέλωσιν, Il. 3.288. Conditions of which the conclusion is vague are sometimes regarded as interrogative, e. g. ἀναπεπταμένα_ς ἔχον α?νέρες, εἴ τιν᾽ ἑταίρων | ἐκ πολέμου φεύγοντα σαώσειαν, they held the gates open, in case they might be able to save some fugitive, Il. 12.122; thus often εἴ που or εἴ πως, ‘in the hope that,’ ‘on the chance that,’ etc. —With other particles, εἰ καί, if also (or denoting concession, though), καὶ εἰ (οὐδ᾽ εἰ, μηδ̓ εἰ), even if, denoting opposition; εἴ τε.. εἴ τε (sive.. sive), ὡς εἰ, ὡς εἴ τε, εἰ δή, εἴ περ, εἴ γε (q. v.); in εἰ δ᾽ ἄγε (q. v.), εἰ is probably an interjection.