From these things it follows, that in questions of difficulty, or such as are thought so, where more satisfactory evidence cannot be had, or is not seen; if the result of examination be, that there appears upon the whole, any even the lowest presumption on one side, and none on the other, or a greater presumption on one side, though in the lowest degree greater; this determines the question, even in matters of speculation. In matters of practice, it will lay us under an absolute and formal obligation, in point of prudence and of interest, to act upon that presumption or low probability, though it be so low as to leave the mind in very great doubt which is the truth. For surely a man is as really bound in prudence to do what upon the whole, according to the best of his judgment, appears to be for his happiness,[9] as what he certainly knows to be so. Further, in questions of great consequence, a reasonable man will think it concerns him to remark lower probabilities and presumptions than these; such as amount to no more than showing one side of a question to be as supposable and credible as the other: nay, such even as but amount to much less than this. For numberless instances might be mentioned respecting the common pursuits of life, where a man would be thought, in a literal sense, distracted, who would not act, and with great application too, not only upon an even chance, but upon much less, and where the probability or chance was greatly against his succeeding.[10] It is not my design to inquire further into the nature, the foundation, and measure of probability; or whence it proceeds that _likeness_ should beget that presumption, opinion, and full conviction, which the human mind is formed to receive from it, and which it does necessarily produce in every one; or to guard against the errors, to which reasoning from analogy is liable. This belongs to the subject of Logic; and is a part of that subject which has not yet been thoroughly considered. Indeed I shall not take upon me to say, how far the extent, compass, and force, of analogical reasoning, can be reduced to general heads and rules; and the whole be formed into a system. But though so little in this way has been attempted by those who have treated of our intellectual powers, and the exercise of them; this does not hinder but that we may be, as we unquestionably are, assured, that analogy is of weight, in various degrees, towards determining our judgment and our practice. Nor does it in any wise cease to be of weight in those cases, because persons, either given to dispute, or who require things to be stated with greater exactness than our faculties appear to admit of in practical matters, may find other cases in which it is not easy to say, whether it be, or be not, of any weight; or instances of seeming analogies, which are really of none. It is enough to the present purpose to observe, that this general way of arguing is evidently natural, just, and conclusive.