William Watson Goodwin, Syntax of the Moods and Tenses of the Greek Verb

---

[*] 415. A peculiar form of potential indicative without ἄν consists of an infinitive depending on the imperfect of a verb of obligation, propriety, or possibility, like ἔδει, χρῆν or ἐχρῆν, εἰκὸς ἦν, or προσῆκεν. This expression refers to past or present time, and generally implies a denial of the action of the infinitive. Thus ἔδει τοῦτον ἀποθανεῖν in this idiomatic use means he ought to have perished (but did not); ἔδει ἡμᾶς τοῦτο ποιεῖν means we ought to be doing this (but we are not) or we ought to have done this (but we did not do it). This combination contains in other words what might have been expressed substantially by a past indicative with ἄν of the verb of the infinitive, qualified by an adverb or other expression denoting obligation, propriety, or possibility: thus ἔδει τοῦτον ἀποθανεῖν is (as a construction) equivalent to οὗτος δικαίως (or ἀξίως) ἂν ἀπέθανεν, he would justly have perished, and εἰκὸς ἦν σε τοῦτο παθεῖν is equivalent to τοῦτο εἰκότως ἂν ἔπαθες, you would properly have suffered this (implying οὐκ ἔπαθες). Strictly, the expression involves also an unreal protasis, as (in the last case) εἰ τὸ εἰκὸς ἔπαθες, which with the apodosis τοῦτο ἔπαθες ἄν appears substantially in εἰκὸς ἦν σε τοῦτο παθεῖν. (See 511.)

When the present infinitive is used, the expression is present or past; with the aorist infinitive it is always past.