It is not too much to require that what the wisest of mankind, those who are best entitled to trust their own judgment, find necessary to warrant their relying on it, should be submitted to by that miscellaneous collection of a few wise and many foolish individuals, called the public. The most intolerant of churches, the Roman Catholic Church, even at the canonisation of a saint, admits, and listens patiently to, a "devil's advocate." The holiest of men, it appears, cannot be admitted to posthumous honours, until all that the devil could say against him is known and weighed. If even the Newtonian philosophy were not permitted to be questioned, mankind could not feel as complete assurance of its truth as they now do. The beliefs which we have most warrant for, have no safeguard to rest on, but a standing invitation to the whole world to prove them unfounded. If the challenge is not accepted, or is accepted and the attempt fails, we are far enough from certainty still; but we have done the best that the existing state of human reason admits of; we have neglected nothing that could give the truth a chance of reaching us: if the lists are kept open, we may hope that if there be a better truth, it will be found when the human mind is capable of receiving it; and in the meantime we may rely on having attained such approach to truth, as is possible in our own day. This is the amount of certainty attainable by a fallible being, and this the sole way of attaining it.
Strange it is, that men should admit the validity of the arguments for free discussion, but object to their being "pushed to an extreme;" not seeing that unless the reasons are good for an extreme case, they are not good for any case. Strange that they should imagine that they are not assuming infallibility, when they acknowledge that there should be free discussion on all subjects which can possibly be _doubtful_, but think that some particular principle or doctrine should be forbidden to be questioned because it is _so certain_, that is, because _they are certain_ that it is certain. To call any proposition certain, while there is any one who would deny its certainty if permitted, but who is not permitted, is to assume that we ourselves, and those who agree with us, are the judges of certainty, and judges without hearing the other side.