Letters 113.17

Every living thing acts of itself; but virtue does nothing of itself; it must act in conjunction with man. All living things either are gifted with reason, like men and gods, or else are irrational, like beasts and cattle. Virtues, in any case, are rational; and yet they are neither men nor gods; therefore they are not living things.

Seneca, Letters to Lucilius 113.17, translated by Richard Mott Gummere