1. Thus no one doubts, when coming to the intersection of two roads, he sees a sign-post, on one of whose pointers is written "To London," and on the other "To Windsor," no one hesitates to believe that the information thus conveyed to him is true; because he is aware that those who give it are competent to do so, and that none similarly competent will gainsay it. 2. Again, no one doubts that the sun rises and sets once in every twenty-four hours; no one doubts that he so rose and set yesterday. Every one is ready to affirm the certainty of these two facts, but very few can do so, in any great degree, from their own experience; but they help the lack of this by that of their neighbors. Neither is it necessary that they should have any near, nor even the most remote, idea of the personality of those on whose testimony they thus implicitly rely; it suffices they are sure, whoever they may be, they have the right qualifications for testifying in the way they do, and that no one so qualified can contradict their evidence, or dream of doing so. The above are examples of the criterion of truth, applied to the ideas and proceedings of ordinary life. It will be seen therefrom, first that mankind have in all ages been educated in an acceptance of its principle, according to my definition of it, the principle, namely, of an indubitable certainty of truth, resulting from the unanimous assent to some idea of all who are thought by self and neighbors competent to pronounce thereon; possibly too they may be said to have been educated in some imperfect theoretical appreciation of this principle. It will secondly be seen therefrom, that the two kinds of unanimity which I have predicated as essential to the proper use and results of this criterion, an unanimity, namely, on the part of the supposed good judges of certain descriptions of truth, who may be called the adepts or knowing ones imagined by the public; and again an unanimity on the part of the public itself in interpreting and adopting their opinion; it will be seen, I say, that this double unanimity is perfectly attainable, nay, perfectly attained, and that too so extensively, as to constitute a common and familiar occurrence on all manner of occasions of daily life. I will now give instances of their similar use of it in directing their judgments on philosophical questions. 3. Very few of the public are able to examine the proof of any of the theorems of Euclid, yet there is none of them who would think of seriously doubting the truth of anything contained in that book, the ground of their confidence being solely their knowledge of the fact, that the learned in these matters have unanimously so decided.