Plato, Laws 720b

πάνυ μὲν οὖν. ἐάντε γε ἐλεύθεροι ὦσιν ἐάντε δοῦλοι, κατʼ ἐπίταξιν δὲ τῶν δεσποτῶν καὶ θεωρίαν καὶ κατʼ ἐμπειρίαν τὴν τέχνην κτῶνται, κατὰ φύσιν δὲ μή, καθάπερ οἱ ἐλεύθεροι αὐτοί τε μεμαθήκασιν οὕτω τούς τε αὑτῶν διδάσκουσι παῖδας. θείης ἂν ταῦτα δύο γένη τῶν καλουμένων ἰατρῶν; πῶς γὰρ οὔ; ἆρʼ οὖν καὶ συννοεῖς ὅτι, δούλων καὶ ἐλευθέρων

We do. These, whether they be free-born or slaves, acquire their art under the direction of their masters, by observation and practice and not by the study of nature—which is the way in which the free-born doctors have learnt the art themselves and in which they instruct their own disciples. Would you assert that we have here two classes of what are called doctors? Certainly. You are also aware that, as the sick folk in the cities comprise both slaves and free men,