Symposiacs (1.1.3)

And when you affirmed that none ought to oppose what Crato said, but determine what sorts of philosophical topics were to be admitted as fit companions at a feast, and so avoid that just and pleasant taunt put upon the wrangling disputers of the age,

Come now to supper, that we may contend;

and when you seemed concerned and urged us to speak to that head, I first replied: Sir, we must consider what company we have; for if the greater part of the guests are learned men,—as for instance, at Agatho’s entertainment, men like Socrates, Phaedrus, Pausanias, Euryximachus; or at Callias’s board, Charmides, Antisthenes, Hermogenes, and the like,—we will permit them to philosophize, and to mix Bacchus with the Muses as well as with the Nymphs; for the latter make him wholesome and gentle to the body, and the other pleasant and agreeable to the soul. And if there are some few illiterate persons present, they, as mute consonants with vowels, in the midst of the other learned, will participate in a voice not altogether inarticulate and insignificant. But if the greater part consists of such who can better endure the noise of any bird, fiddle-string, or piece of wood than the voice of a philosopher, Pisistratus hath shown us what to do; for being at difference with his sons, when he heard his enemies rejoiced at it, in a full assembly he declared that he had endeavored to persuade his sons to submit to him, but since he found them obstinate, he was resolved to yield and submit to their humors. So a philosopher, midst those companions that slight his excellent discourse, will lay aside his gravity, follow them, and comply with their humor as far as decency will permit; knowing very well that men cannot exercise their rhetoric unless they speak, but may their philosophy even whilst they are silent or jest merrily, nay, whilst they are piqued upon or repartee. For it is not only (as Plato says) the highest degree of injustice not to be just and yet seem so; but it is the top of wisdom to philosophize, yet not appear to do it; and in mirth to do the same with those that are serious, and yet seem in earnest. For as in Euripides, the Bacchae, though unprovided of iron weapons and unarmed, wounded their invaders with their boughs, thus the very jests and merry talk of true philosophers move and correct in some sort those that are not altogether insensible.