But those who, in the opinion of Celsus, resemble the workers in wool in private houses, and the leather-cutters, and fullers, and uneducated rustics, will, he alleges, in the presence of father or teachers be unwilling to speak, or unable to explain to the boys anything that is good. In answer to which, we would say, What kind of father, my good sir, and what kind of teacher, do you mean? If you mean one who approves of virtue, and turns away from vice, and welcomes what is better, then know, that with the greatest boldness will we declare our opinions to the children, because we will be in good repute with such a judge.
But if, in the presence of a father who has a hatred of virtue and goodness, we keep silence, and also before those who teach what is contrary to sound doctrine, do not blame us for so doing, since you will blame us without good reason. You, at all events, in a case where fathers deemed the mysteries of philosophy an idle and unprofitable occupation for their sons, and for young men in general, would not, in teaching philosophy, make known its secrets before worthless parents; but, desiring to keep apart those sons of wicked parents who had been turned towards the study of philosophy, you would observe the proper seasons, in order that the doctrines of philosophy might reach the minds of the young men.
And we say the same regarding our teachers. For if we turn (our hearers) away from those instructors who teach obscene comedies and licentious iambics, and many other things which neither improve the speaker nor benefit the hearers (because the latter do not know how to listen to poetry in a philosophic frame of mind, nor the former how to say to each of the young men what tends to his profit), we are not, in following such a course, ashamed to confess what we do. But if you will show me teachers who train young men for philosophy, and who exercise them in it, I will not from such turn away young men, but will try to raise them, as those who have been previously exercised in the whole circle of learning and in philosophical subjects, to the venerable and lofty height of eloquence which lies hid from the multitude of Christians, where are discussed topics of the greatest importance, and where it is demonstrated and shown that they have been treated philosophically both by the prophets of God and the apostles of Jesus.
Source: Against Celsus (New Advent)