He who knows only his own side of the case knows little of that. No one may have been able to refute them. But if he is equally unable to refute the reasons on the opposite side, he has no ground for preferring either opinion. Nor is it enough that he should hear the opinions of adversaries from his own teachers, presented as they state them, and accompanied by what they offer as refutations. He must be able to hear them from persons who actually believe them.