Galen, On the Natural Faculties
1.14.52-53 (tr. A.J. Brock):
Now people of the present day do not begin by getting a clear comprehension of these sects, as well as of the better ones, thereafter devoting a long time to judging and testing the true and false in each of them; despite their ignorance, they style themselves, some "physicians" and others "philosophers." No wonder, then, that they honour the false equally with the true. For everyone becomes like the first teacher that he comes across, without waiting to learn anything from anybody else. And there are some of them, who, even if they meet with more than one teacher, are yet so unintelligent and slow-witted that even by the time they have reached old age they are still incapable of understanding the steps of an argument. In the old days such people used to be set to menial tasks. What will be the end of it God knows!
ἀλλ᾿ οἱ νῦν ἄνθρωποι, πρὶν καὶ ταύτας ἐκμαθεῖν τὰς αἱρέσεις καὶ τὰς ἄλλας τὰς βελτίους κἄπειτα χρόνῳ πολλῷ κρῖναί τε καὶ βασανίσαι τὸ καθ᾿ ἑκάστην αὐτῶν ἀληθές τε καὶ ψεῦδος, οἱ μὲν ἰατροὺς ἑαυτούς, οἱ δὲ φιλοσόφους ὀνομάζουσι μηδὲν εἰδότες. οὐδὲν οὖν θαυμαστὸν ἐπίσης τοῖς ἀληθέσι τὰ ψευδῆ τετιμῆσθαι. ὅτῳ γὰρ ἂν ἕκαστος πρώτῳ περιτύχῃ διδασκάλῳ, τοιοῦτος ἐγένετο, μὴ περιμείνας μηδὲν ἔτι παρ᾿ ἄλλου μαθεῖν. ἔνιοι δ᾿ αὐτῶν, εἰ καὶ πλείοσιν ἐντύχοιεν, ἀλλ᾿ οὕτω γ᾿ εἰσὶν ἀσύνετοί τε καὶ βραδεῖς τὴν διάνοιαν, ὥστε καὶ γεγηρακότες οὔπω συνιᾶσιν ἀκολουθίαν λόγου. πάλαι δὲ τοὺς τοιούτους ἐπὶ τὰς βαναύσους ἀπέλυον τέχνας. ἀλλὰ ταῦτα μὲν ἐς ὅ τι τελευτήσει θεὸς οἶδεν.