The question, What is the Criterion of Truth?--that is, What are the proper means of distinguishing whether anything that is asserted to be true is so or not? claims immediate notice, because such a criterion exists, and the new philosophy necessarily appeals to it when it comes before the public, while it has shown with what effect it can do so, in the case of those of its branches--namely, the purely material and the mathematical, that flourish in society. Premising that it is a way of certifying truth that has been immemorially used by mankind in their daily affairs, and which they have always, to some extent, instinctively transferred to their judgments in philosophy, and that it is the only possible general and summary criterion of truth, I may describe it as consisting in the unanimous assent to some idea or assertion of all who are thought competent to pronounce concerning it. Viewed in connection with the thing it verifies, and the parties who use it, the criterion may be thus represented: Any idea, assertion, or opinion, must, by any inquirer, be found true, when he perceives it to be such as would be unanimously assented to by all presumably competent judges of the kind of truth to which it refers. So that those who use this criterion, and are convinced of the truth of anything through its medium--a proceeding which I have represented as common and habitual to mankind--in thereby pronouncing certain supposed persons to be judges of truth in the said matter, claim themselves to be also judges of it in the matter of so pronouncing. The acts of judgment they thus tacitly challenge to themselves may be said to be to the following effect:--1. They assign the qualifications that constitute competency for a certain function. 2. They decide that there are persons in the community answering to this character. 3. They opine that the view such persons take or would take, imports an assertion of the truth of the idea in question. 4. They accredit that view with being strictly one, supposing that all qualified to arbitrate would acquiesce and agree in the same. 5. They attribute to themselves a similar unanimity. 6. They assume the sufficiency of their own judgment to make all the above conclusions. These assumptions on their part, so complicated in description, are simple enough in performance. It is plain that mankind--more properly here to be called the public--simply attach themselves to some opinion which they find current in society; while, however, the assumptions I have just described are, in their full measure, but a necessary consequence of their so doing, doubtless their so doing must itself have been dictated by some kind of anticipation of them, but this may, to any degree, have been vague, undetermined, partial, and imperfect.