Letters 124.20

But, not to weary you, a certain sort of good will be found in a dumb animal, and a certain sort of virtue, and a certain sort of perfection—but neither the Good, nor virtue, nor perfection in the absolute sense. For this is the privilege of reasoning beings alone, who are permitted to know the cause, the degree, and the means. Therefore, good can exist only in that which possesses reason.

Seneca, Letters to Lucilius 124.20, translated by Richard Mott Gummere