De Plantatione

Who, indeed, is there who does not know that of two opposite things, when one kind is suitable to most people, the other kind must of necessity be suited to some? As, for instance, white and black are two opposite colours: if white is suitable both to good and to bad things, then black must also be necessarily equally suitable to both, and not to one of the two alone. And, again, to be sober and to be drunk are two opposite things; accordingly, both bad men and good, as the ancient proverb says, partake of sobriety; therefore, also, drunkenness is suitable to both classes. Therefore the virtuous man will get drunk without losing any of his virtue by it.

But if, like persons before a court of justice, one must bring forward not only such proofs as are in accordance with the rules of art, but those too which have no connection with art, one of which is proof by testimony, we will then produce many sons of physicians and philosophers of high repute to give evidence, not by words alone, but also by writings.