ence is based on the principle of resemblance. But then we must ask, What is the ground of the principle of the uniformity of nature? And to this Hume's answer in the Inquiry, briefly, is custom.[1] And in the formation of this principle of custom or habit, so far as the question of causation is concerned, there comes into play the law of contiguity as well as that of resemblance. The fact that contiguity is not mentioned in the definitions of cause given in the Inquiry,[2] does not seem particularly significant. Succession is mentioned in these definitions as well as resemblance. The definitions are briefer in the Inquiry, and this may account for the less precise form of expression. With regard to the statement, that in the later work the distinction between cause as a natural, and cause as a philosophical relation is no longer observed, I think something may be said on the other side. Some writers maintain that the position of Hume on the question of causation is the same, or practically the same, as that of Kant.[3] But this probably arises from a misconception with regard to Kant's theory of knowledge.[4]
The doctrine of belief is identical in the two works. Again, however, there are some differences in the manner of treatment. In the Inquiry, the mode of expression is more hesitating and cautious than in the Treatise. This may probably be explained on the grounds: (1) That Hume has now lost a little of his former youthful ardor, and thus has acquired a more judicial balance of mind;[5] and (2) that he apparently, after the publication of the Treatise, was sometimes unable to decide whether the only difference between an impression and its idea, or between two ideas of the same impression, was a difference merely in the degrees of force and liveliness.[6]
6. Probability, Necessity or Determinism, and Reason of Animals. To the three sections in the Treatise dealing with probability, there corresponds only one brief section of a few
