单项选择题

No one can be a great thinker who does not realize that as a thinker it is his first duty to follow his intellect to whatever conclusions it may lead. Truth gains more even by the errors of one who, with due study and preparation, thinks for himself, than by the true opinions of those who only hold them because they do not suffer themselves to think. Not that it is solely, or chiefly, to form great thinkers that freedom of thinking is required. On the contrary, it is as much or even more indispensable to enable average human beings to attain the mental quality which they are capable of. There have been, and may again be, great individual thinkers in a general atmosphere of mental slavery. But there never has been, nor ever will be, in that atmosphere an intellectually active people. While any people has made a temporary approach to such a character, it has been because the dread of heterodox(非正统的) thinking was for a time suspended. Where there is an unspoken convention that principles are not to be disputed; where the discussion of the greatest questions which can occupy humanity is considered to be closed, we cannot hope to find that generally high scale of mental activity which has made some periods of history so remarkable. Never when prolonged arguments avoided the subjects which are large and important enough to rouse enthusiasm was the mind of a people stirred up from its foundations and the impulse given which raised even persons of the most ordinary intellect to something of thinking beings. 　　He who knows only his own side of the case knows little of that. His reasons may be good, and no one may have been able to refute them. But if he is equally unable to refute the reasons on the opposite side, and if he does not so much as know what they are, he has no ground for preferring either opinion. The rational position for him would be suspension of judgment, and unless he contents himself with that, he is either led by authority, or adopts, like the generality of the world, the side to which he feels the most inclination. Nor is it enough that he should hear the arguments of opponents from his own teachers ,presented as they state them, and accompanied by what they offer as refutations. That is not the way to do justice to the arguments, or bring them into real contact with his own mind. He must be able to hear them from persons who actually believe them; who defend them in earnest, and do their very utmost for them. He must know them in their seemingly reasonable and persuasive form: he must feel the whole force of the difficulty which the true view of the subject has to encounter and dispose of; otherwise he will never really possess himself of the portion of truth which meets and removes that difficulty. Ninety-nine in a hundred of what are called educated men are in this condition, and even of those who can argue fluently for their opinions. Their conclusion may be true, but it might be false for anything they know. They have never thrown themselves into the mental position of those who think differently from them and considered what such persons may have to say. The fundamental criterion for a great thinker consists in his