The Republic by Plato Part 4 Page 36

object was in selecting our soldiers, and educating them in music and gymnastic; we were contriving influences which would prepare them to take the dye of the laws in perfection, and the colour of their opinion about dangers and of every other opinion was to be indelibly fixed by their nurture and training, not to be washed away by such potent lyes as pleasure — mightier agent far in washing the soul than any soda or lye; or by sorrow, fear, and desire, the mightiest of all other solvents. And this sort of universal saving power of true opinion in conformity with law about real and false dangers I call and maintain to be courage, unless you disagree.

But I agree, he replied; for I suppose that you mean to exclude mere uninstructed courage, such as that of a wild beast or of a slave — this, in your opinion, is