We must, therefore, leave open the question whether the time-order of events in one causal route can be defined in terms of causal laws. FOOTNOTES: [71] Eddington, op. cit., p. 137. [72] This question (as well as various others) is ably discussed in a valuable article by Hans Reichenbach, Kausalstruktur der Welt und der Unterschied von Vergangenheit und Zukunft, Sitzungsberichte der Bayerischen Akademie der Wissenschaften, mathematisch-natur-wissenschaftliche Abteilung, 1925, pp. 133-175. [73] Op. cit., pp. 52-3. [74] lb., p. 33. [Pg 382] CHAPTER XXXVII PHYSICS AND NEUTRAL MONISM IN this chapter, I wish to define the outcome of our analysis in regard to the old controversy between materialism and idealism, and to make it clear wherein our theory differs from both. So long as the views set forth in previous chapters are supposed to be either materialistic or idealistic, they will seem to involve inconsistencies, since some seem to tend in the one direction, some in the other. For example, when I say that my percepts are in my head, I shall be thought materialistic; when I say that my head consists of my percepts and other similar events, I shall be thought idealistic. Yet the former statement is a logical consequence of the latter. Both materialism and idealism have been guilty, unconsciously and in spite of explicit disavowals, of a confusion in their imaginative picture of matter. They have thought of the matter in the external world as being represented by their percepts when they see and touch, whereas these percepts are really part of the matter of the percipient's brain. By examining our percepts it is possible—so I have contended—to infer certain formal mathematical properties of external matter, though the inference is not demonstrative or certain. But by examining our percepts we obtain knowledge which is not purely formal as to the matter of our brains. This knowledge, it is true, is fragmentary, but so far as it goes it has merits surpassing those of the knowledge given by physics.