and with respect to modes, the only question of importance is that of abstract, or rather general, ideas. From some incidental references to this subject in section xii of the Inquiry,[1] we find that, on the question of abstract or general ideas, the position of the two works is exactly the same. The most probable reason for all of these omissions in the Inquiry is Hume's desire to give a brief, clear, and popular exposition of his philosophical system, such as would win the ear of the public and acquire fame for himself as a philosophical writer. To this may be added, as possibly an additional reason for the omissions concerning relations, that Hume, before the publication of the Inquiry, may have become conscious of some of the difficulties involved in his doctrine on this subject, and consequently, have made these omissions purposely, in order to avoid them.[2]
4. Space, Time, and Mathematics. As has already been said, Part II of the Treatise is omitted in the Inquiry, and consequently the discussion on space and time. But in the twelfth section and appended notes, we find some statements which clearly imply that the view of space and time as held in the later work is similar to that which had appeared in the earlier. There is implied the same process of derivation of these ideas;[3] there are no abstract or general ideas;[4] and space and time are not infinitely divisible.[5] The treatment of mathematics follows on the consideration of space and time, and is much fuller in the Treatise than in the Inquiry. But on this subject Hume is evidently not consistent with himself, either in the two works taken together or in either of them taken separately. In the earlier parts of the Treatise, arithmetic and algebra are spoken of as being exact and certain sciences.[6] But when we come to Part IV,[7] because of "our fallible and uncertain faculties," "all knowledge resolves itself into probability, and becomes at last of the same nature with that evidence which we employ in common life." Geometry,[8] however, throughout the Treatise, is regarded as an inexact science, because its first
