Herbert Weir Smyth, A Greek Grammar for Colleges

εἰ ταῦτα ποιοίης, καλῶς ἂν ποιοίης or εἰ ταῦτα ποιήσειας, καλῶς ἂν ποιήσειας if you should do this, you would do well.

““εἴης φορητὸς οὐκ ἄν, εἰ πρά_σσοις καλῶς” thou wouldst be unendurable shouldst thou be prosperous” A. Pr. 979, εἰ δ᾽ ἀναγκαῖον εἴη ἀδικεῖν ἢ ἀδικεῖσθαι, ἑλοίμην ἂν μᾶλλον ἀδικεῖσθαι ἢ ἀδικεῖν but if it should be necessary to do wrong or be wronged, I should prefer to be wronged than to do wrong P. G. 469c, ““δεινὰ ἂν εἴην εἰργασμένος, . . . εἰ λίποιμι τὴν τάξιν” I should be in the state of having committed a dreadful deed, if I were to desert my post” P. A. 28d.

a. Anything physically impossible may be represented as supposable, hence this construction may be used of what is contrary to fact. Thus, ““φαίη δ᾽ ἂν ἡ θανοῦσά γ᾽ ει᾽ φωνὴν λάβοι” the dead would speak if gifted with a voice” S. El. 548. Cp. A. Ag. 37, P. Pr. 361a, Eu. 299 d, and see 2311 a, 2322 c.