pages in the Inquiry. This is a sort of incomplete summary of the former treatment, and really contains nothing new. It may be remarked, however, that in both works, Hume expresses himself to the effect that his doctrine of chance goes to confirm his doctrine of causation and belief.[1] After the subject of necessary connection is disposed of, the order of discussion differs considerably in the two works, as has already been indicated. Mr. Selby-Bigge[2] thinks that the omission, in the Inquiry, of the section on general rules is a part of Hume's policy to evade a difficulty arising from his theory of causation. This may be so, or, on the other hand, it may be for the sake of brevity. Concerning the relation between the two separate treatments of liberty and necessity, see Mr. Selby-Bigge's introduction to Humes Inquiries.[3] The discussion on the reason of animals is practically the same in the two works, and Hume thinks his explanation of this question goes to confirm his doctrine of reasoning with regard to man.[4]
7. Ideas of Material Substance and an External World. In the Inquiry there is no discussion of the idea of material substance, but the same view as that of the Treatise follows here, logically, and by implication, (1) This idea is logically impossible, because Hume's criterion of the validity of any idea still remains in full force in the later work.[5] (2) It is actually unnecessary, for Hume asserts that the qualities of "solidity," "extension," and "motion" are qualities "complete in themselves."[6] And these qualities—the primary—are on the same basis as the secondary qualities.[7] The idea of the existence of an external world is discussed in the Inquiry, but much more briefly and incompletely than in the Treatise ; and apparently without any change of standpoint. The account of the psychological process of arriving at the vulgar hypothesis of external existence is omitted, but all the main points of the doctrine as presented in the Treatise are implied in the Inquiry, as we may see by the following comparison:—Treatise: (1)
