Plato, Laws 820c

ἐν οἷς αὖ πολλὰ ἁμαρτήματα ἐκείνων ἀδελφὰ ἡμῖν ἐγγίγνεται τῶν ἁμαρτημάτων. ποῖα δή; τὰ τῶν μετρητῶν τε καὶ ἀμέτρων πρὸς ἄλληλα ᾗτινι φύσει γέγονεν. ταῦτα γὰρ δὴ σκοποῦντα διαγιγνώσκειν ἀναγκαῖον ἢ παντάπασιν εἶναι φαῦλον, προβάλλοντά τε ἀλλήλοις ἀεί, διατριβὴν τῆς πεττείας πολὺ χαριεστέραν πρεσβυτῶν διατρίβοντα, φιλονικεῖν ἐν ταῖς τούτων ἀξίαισι σχολαῖς.

in which we find many errors arising that are nearly akin to the errors mentioned. What are they? Problems concerning the essential nature of the commensurable and the incommensurable. For students who are not to be absolutely worthless it is necessary to examine these and to distinguish the two kinds, and, by proposing such problems one to another, to compete in a game that is worthy of them,—for this is a much more refined pastime than draughts for old men.