E.C. Marchant, Commentary on Thucydides: Book 3

παραδείγμασι τοῖς προγιγνομένοις χ.—‘drawing our proofs (that they were no longer πιστοί) from what was previously happening,’ i.e. ‘taking warning from the line of action that they had adopted.’ παράδειγμα is an example by which a conclusion may be supported. τοῖς προγιγνομένοις=‘the line of conduct that they were pursuing previously, and had not ceased to pursue.’ (The aor. or perf. partic. is conjectured here as in I. 23 τοὺς Ἀθηναίους ἡγοῦμαι μεγάγους γιγνομένους . . ἀναγκάσαι ἐς τὸ πολεμεῖν, which alludes to the conduct of Athens during the same period—between the formation of the Confederacv to the beginning of the war—from a different point of view. In both places the pres. partic., describing something still in progress, seems better.)

οὐ γὰρ εἰκὸς ἦν . . . μὴ δρᾶσαι τοῦτο—to understand this sentence, it is necessary to realize that δρᾶσαι refers, not to the future, but to the past, as in c. 40, 5 ἐνθυμηθέντες ἂ είκὸς ἦν αὐτοὺς ποιῆσαι κρατήσαντας ὑμῶν. The sense is ‘it was not likely that they . . would not have treated those who were left in this way, if only they had found any opportunity.’ We should have been ‘enslaved’ had circumstances been favourable to Athens: cf. I. 98 (ἐδουλώθησαν) καὶ τῶν ἄλλων ὡς ἑκάστῃ ξυνέβη. (Dobree's δυνηθεῖεν makes the ref. to the future.)