In praising a speaker we must be generous, but in believing his words cautious; as touching the style and the delivery of the performers, we should observe with a kindly and simple mind; but as for the utility and the truth of what they say, we must play the keen and heartless critics, that the speakers may feel no hatred, yet their words may do no harm. For we unwittingly receive into our minds a great many false and vicious doctrines by feeling goodwill and confidence towards the speakers.
δεῖ δὲ τὸν μὲν ἔπαινον ἀφελῶς τοῖς λέγουσι τὴν δὲ πίστιν εὐλαβῶς προΐεσθαι τοῖς λόγοις, καὶ τῆς μὲν λέξεως καὶ προφορᾶς τῶν ἀγωνιζομένων εὐμενῆ καὶ ἁπλοῦν εἶναι θεατήν, τῆς δὲ χρείας καὶ τῆς ἀληθείας τῶν λεγομένων ἀκριβῆ καὶ πικρὸν ἐξεταστήν, ἵνʼ οἱ μὲν λέγοντες μὴ μισῶσιν, οἱ δὲ λόγοι μὴ βλάπτωσιν· ὡς πολλὰ ψευδῆ καὶ πονηρὰ δόγματα λανθάνομεν εὐνοίᾳ καὶ πίστει τῇ πρὸς τοὺς λέγοντας ἐνδεχόμενοι.
On Listening to Lectures 41a – b