Since the foregoing paragraphs were written Mr. Russell has published, in The Monist of July, 1915, a paper on “The Ultimate Constituents of Matter” which supplements his conception of extra-mental reality and adds to his arguments against the idealistic account of physical reality. But for an obstinate error of ‘common sense’ Russell would assent, he declares, to its theory of extra-mental reality. Common sense is clearly correct in believing that what we see is physical and is as clearly at fault in believing that what is physical must be persistent (p. 401).[1] Russell holds first, that sense-data—what we see, hear, and touch—are “extra-mental … and among the ultimate constituents of matter”[2] and second in opposition to common sense that “the persistent particles of mathematical physics” are “logical constructions” (p. 402). Space, so far from being “all-embracing,’ is a largely individual affair. Each man’s extra-mental object occupies a place (and time) of its own.
The theory of a multitude of three-dimensional spaces—not to name the “crude space of six dimensions” (p. 416)—might be argued for, Russell suggests, by the aid of symbolic logic, but the argument would be too difficult and too technical to be embarked upon in this article (p. 415.) The extra-mental reality of sense-data, so far as he argues it at all, he bases on two distinctions: on the fact that ‘what I see,’ and ‘what I hear’ are to be distinguished from ‘seeing’ and ‘hearing’ (p. 404), and on the fact that ”colors and noises are not mental in the sense of having that … peculiarity which belongs to beliefs and wishes and volitions” (p. 405). But it is clear that the first of these arguments tells against solipsism only and that the second does not necessarily prove more than the fact that there is a difference between perceptual experience and other types of consciousness. Accordingly, the reader comes with great surprise upon the concluding sentences in which Mr. Russell, while disclaiming the conviction that his theory “is certainly true,” adds that it “may be true” and that this is “more than can be said for any other theory” (p. 417), except that of Leibniz which he regards as “closely analogous” to his own. The idealist, as the earlier paragraphs of this discussion have indicated, concurs in Russell’s criticism of other realistic systems and may well agree that, given Russell’s constant, unjustified assumption of existent extra-mental reality, his account of it “may be true.” But the idealistic reader will also insist that Mr. Russell’s consideration
