Aristotle: Analytica Priora (Prior Analytics)

καὶ βαδίζειν καὶ μὴ βαδίζειν, καὶ ἐπιστήμων τἀγαθοῦ καὶ τοῦ μὴ ἀγαθοῦ ἐστί)· φάσις δὲ καὶ ἀπόφασις οὐχ ὑπάρχουσιν αἱ ἀντικείμεναι ἅμα τῷ αὐτῷ. Ὥσπερ οὖν οὐ ταὐτό ἐστι τὸ μὴ ἐπίστασθαι τἀγαθὸν καὶ ἐπίστασθαι τὸ μὴ ἀγαθόν, οὐδ᾿ εἶναι μὴ ἀγαθὸν καὶ μὴ εἶναι ἀγαθὸν ταὐτόν. Τῶν γὰρ ἀνὰ λόγον ἐὰν θάτερα ᾖ ἕτερα, καὶ θάτερα. Οὐδὲ τὸ εἶναι μὴ ἴσον καὶ τὸ μὴ εἶναι ἴσον· τῷ μὲν γὰρ ὑπόκειταί τι, τῷ ὄντι μὴ ἴσῳ, καὶ τοῦτ᾿ ἔστι τὸ ἄνισον, τῷ δ᾿ οὐδέν. Διόπερ ἴσον μὲν ἢ ἄνισον οὐ πᾶν, ἴσον δ᾿ ἢ οὐκ ἴσον πᾶν. Ἔτι τὸ ἔστιν οὐ λευκὸν ξύλον καὶ οὐκ ἔστι λευκὸν ξύλον οὐχ ἅμα ὑπάρχει. Εἰ γάρ ἐστι ξύλον οὐ λευκόν, ἔσται ξύλον· τὸ δὲ μὴ ὂν λευκὸν ξύλον οὐκ ἀνάγκη ξύλον εἶναι. Ὥστε φανερὸν ὅτι οὐκ ἔστι τοῦ ἔστιν ἀγαθόν τὸ ἔστιν οὐκ ἀγαθόν ἀπόφασις. Εἰ οὖν κατὰ παντὸς ἑνὸς ἢ φάσις ἢ ἀπόφασις ἀληθής, εἰ μή ἐστιν ἀπόφασις, δῆλον ὡς κατάφασις ἄν πως εἴη. Καταφάσεως δὲ πάσης ἀπόφασίς ἐστι· καὶ ταύτης ἄρα τὸ οὐκ ἔστιν οὐκ ἀγαθόν. Ἔχει δὲ τάξιν τήνδε πρὸς ἄλληλα. Ἔστω τὸ εἶναι ἀγαθὸν ἐφ᾿ οὗ Α, τὸ δὲ μὴ εἶναι ἀγαθὸν ἐφ᾿ οὗ Β, τὸ δὲ εἶναι μὴ ἀγαθὸν ἐφ᾿ οὗ Γ, ὑπὸ τὸ Β, τὸ δὲ μὴ εἶναι μὴ ἀγαθὸν ἐφ᾿ οὗ Δ, ὑπὸ τὸ Α. Παντὶ δὴ ὑπάρξει ἢ τὸ Α ἢ τὸ Β, καὶ οὐδενὶ τῷ αὐτῷ· καὶ ἢ τὸ Γ ἢ τὸ Δ, καὶ οὐδενὶ τῷ αὐτῷ. Καὶ ᾧ τὸ Γ, ἀνάγκη τὸ Β παντὶ ὑπάρχειν. Εἰ γὰρ ἀληθὲς εἰπεῖν ὅτι οὐ λευκόν, καὶ ὅτι οὐκ ἔστι λευκὸν ἀληθές· ἀδύνατον γὰρ ἅμα εἶναι λευκὸν καὶ εἶναι μὴ λευκόν, ἢ εἶναι ξύλον οὐ λευκὸν καὶ εἶναι ξύλον λευκόν, ὥστ᾿ εἰ μὴ ἡ κατάφασις, ἡ ἀπόφασις ὑπάρξει. Τῷ δὲ Β τὸ Γ οὐκ ἀεί· ὃ γὰρ ὅλως μὴ ξύλον, οὐδὲ ξύλον ἔσται οὐ λευκόν. Ἀνάπαλιν τοίνυν, ᾧ τὸ Α, τὸ Δ παντί. Ἢ γὰρ τὸ Γ ἢ τὸ Δ. Ἐπεὶ δ᾿ οὐχ οἷόν τε ἅμα εἶναι μὴ λευκὸν καὶ λευκόν, τὸ Δ ὑπάρξει. Κατὰ γὰρ τοῦ ὄντος λευκοῦ ἀληθὲς εἰπεῖν ὅτι οὐκ ἔστιν οὐ λευκόν. Κατὰ δὲ τοῦ Δ οὐ παντὸς τὸ Α· κατὰ γὰρ τοῦ ὅλως μὴ ὄντος ξύλου οὐκ ἀληθὲς τὸ Α εἰπεῖν,