Aristotle: De Interpretatione (On Interpretation)

τῷ μὲν γὰρ δυνατὸν εἶναι τὸ ἐνδέχεσθαι εἶναι, καὶ τοῦτο ἐκείνῳ ἀντιστρέφει, καὶ τὸ μὴ ἀδύνατον εἶναι καὶ τὸ μὴ ἀναγκαῖον εἶναι· τῷ δὲ δυνατὸν μὴ εἶναι καὶ ἐνδεχόμενον μὴ εἶναι τὸ μὴ ἀναγκαῖον μὴ εἶναι καὶ τὸ οὐκ ἀδύνατον μὴ εἶναι, τῷ δὲ μὴ δυνατὸν εἶναι καὶ μὴ ἐνδεχόμενον εἶναι τὸ ἀναγκαῖον μὴ εἶναι καὶ τὸ ἀδύνατον εἶναι, τῷ δὲ μὴ δυνατὸν μὴ εἶναι καὶ μὴ ἐνδεχόμενον μὴ εἶναι τὸ ἀναγκαῖον εἶναι καὶ τὸ ἀδύνατον μὴ εἶναι. Θεωρείσθω δὲ ἐκ τῆς ὑπογραφῆς ὡς λέγομεν.

δυνατὸν εἶναι οὐ δυνατὸν εἶναι

ἐνδεχόμενον εἶναι οὐκ ἐνδεχόμενον εἶναι

οὐκ ἀδύνατον εἶναι ἀδύνατον εἶναι

οὐκ ἀναγκαῖον εἶναι ἀναγκαῖον μὴ εἶναι

δυνατὸν μὴ εἶναι οὐ δυνατὸν μὴ εἶναι

ἐνδεχόμενον μὴ εἶναι οὐκ ἐνδεχόμενον μὴ εἶναι

οὐκ ἀδύνατον μὴ εἶναι ἀδύνατον μὴ εἶναι

οὐκ ἀναγκαῖον μὴ εἶναι ἀναγκαῖον εἶναι

Τὸ μὲν οὖν ἀδύνατον καὶ οὐκ ἀδύνατον τῷ ἐνδεχομένῳ καὶ δυνατῷ καὶ οὐκ ἐνδεχομένῳ καὶ μὴ δυνατῷ ἀκολουθεῖ μὲν ἀντιφατικῶς, ἀντεστραμμένως δέ· τῷ μὲν γὰρ δυνατὸν εἶναι ἡ ἀπόφασις τοῦ ἀδυνάτου ἀκολουθεῖ, τῇ δὲ ἀποφάσει ἡ κατάφασις· τῷ γὰρ οὐ δυνατὸν εἶναι τὸ ἀδύνατον εἶναι· κατάφασις γὰρ τὸ ἀδύνατον εἶναι, τὸ δ᾿ οὐκ ἀδύνατον εἶναι ἀπόφασις. Τὸ δ᾿ ἀναγκαῖον πῶς, ὀπτέον. Φανερὸν δὴ ὅτι οὐχ οὕτως ἔχει, ἀλλ᾿ αἱ ἐναντίαι ἕπονται· αἱ δ᾿ ἀντιφάσεις χωρίς. Οὐ γάρ ἐστιν ἀπόφασις τοῦ ἀνάγκη μὴ εἶναι τὸ οὐκ ἀνάγκη εἶναι· ἐνδέχεται γὰρ ἀληθεύεσθαι ἐπὶ τοῦ αὐτοῦ ἀμφοτέρας· τὸ γὰρ ἀναγκαῖον μὴ εἶναι οὐκ ἀναγκαῖον εἶναι. Αἴτιον δὲ τοῦ μὴ ἀκολουθεῖν τὸ ἀναγκαῖον ὁμοίως τοῖς