Those philosophers who have divided human reason into _knowledge and probability_, and have defined the first to be _that evidence which arises from the comparison of ideas_, are obliged to comprehend all our arguments from causes or effects under the general term of probability. But though every one be free to use his terms in what sense he pleases; and accordingly, in the precedent part of this discourse, I have followed this method of expression; 'tis however certain, that in common discourse we readily affirm, that many arguments from causation exceed probability, and may be received as a superior kind of evidence. One would appear ridiculous who would say, that 'tis only probable the sun will rise to-morrow, or that all men must die; though 'tis plain we have no further assurance of these facts than what experience affords us. For this reason t'would perhaps be more convenient, in order at once to preserve the common signification of words, and mark the several degrees of evidence, to distinguish human reason into three kinds, viz. _that from knowledge, from proofs, and from probabilities_. By knowledge, I mean the assurance arising from the comparison of ideas. By proofs, those arguments which are derived from the relation of cause and effect, and which are entirely free from doubt and uncertainty. By probability, that evidence which is still attended with uncertainty. 'Tis this last species of reasoning I proceed to examine. Probability or reasoning from conjecture may be divided into two kinds, viz. that which is founded on _chance_, and that which arises from _causes_. We shall consider each of these in order. The idea of cause and effect is derived from experience, which, presenting us with certain objects constantly conjoined with each other, produces such a habit of surveying them in that relation, that we cannot, without a sensible violence, survey them in any other. On the other hand, as chance is nothing real in itself, and, properly speaking, is merely the negation of a cause, its influence on the mind is contrary to that of causation; and 'tis essential to it to leave the imagination perfectly indifferent, either to consider the existence or non-existence of that object which is regarded as contingent. A cause traces the way to our thought, and in a manner forces us to survey such certain objects in such certain relations. Chance can only destroy this determination of the thought, and leave the mind in its native situation of indifference; in which, upon the absence of a cause, 'tis instantly reinstated.