ἔστιν ἄρα ἡ ἀρετὴ ἕξις προαιρετική, ἐν μεσότητι οὖσα τῇ πρὸς ἡμᾶς, ὡρισμένῃ λόγῳ καὶ ᾧ ἂν ὁ φρόνιμος ὁρίσειεν. μεσότης δὲ δύο κακιῶν, τῆς μὲν καθ᾽ ὑπερβολὴν τῆς δὲ κατ᾽ ἔλλειψιν: καὶ ἔτι τῷ τὰς μὲν ἐλλείπειν τὰς δ᾽ ὑπερβάλλειν τοῦ δέοντος ἔν τε τοῖς πάθεσι καὶ ἐν ταῖς πράξεσι, τὴν δ᾽ ἀρετὴν τὸ μέσον καὶ εὑρίσκειν καὶ αἱρεῖσθαι.
Virtue then is a habit of mind concerning choice, consisting in the mean relative to us, determined with reference to reason, as a sensible man would define it. It is a middle ground between two evils: one of excess and one of deficiency; because one of these vices falls short of what is proper and the other goes beyond it, both in passions and in actions, where virtue finds and chooses the mean.
Aristotle,
Ethica Nichomachea, 1106b-1107a. My translation.
est modus in rebus, sunt certi denique fines
quod ultra citraque nequit consistere rectum.
There
is a mean in things, and there are certain boundaries, beyond which and
short of which, virtue is not able to find a place.
Horace,
Sermones I.106-7. My translation.