Institutio Oratoria
Quintilian
Quintilian. Institutio Oratoria, Volume 1-4. Butler, Harold Edgeworth, translator. Cambridge, Mass; London: Harvard University Press, William Heinemann Ltd., 1920-1922.
I have thought it worth while to put my views on this subject quite briefly. For I do not think it necessary even to warn the teacher that both he and his school must be free from the grosser vices. And should there be any father who does not trouble to choose a teacher for his son who is free from the obvious taint of immorality, he may rest assured that all the other precepts, which I am attempting to lay down for the benefit of our youth, will be absolutely useless to him, if he neglects this.
III. I do not think that I should pass by in silence
I do not think that I need waste much time in pointing out how much better it is to absorb the best possible principles, or how hard it is to get rid of faults which have once become engrained; for it places a double burden on the shoulders of the later teacher and the preliminary task of unteaching is harder than that of teaching.