The mention of Spinoza will no doubt suggest to the reader the famous doctrine, which has played so large a part in the subsequent development of philosophical Monism, of the double “aspects” or “attributes” of Reality. It is from Spinoza that modern Monism has learned the view that the mental and physical orders are related as two parallel but distinct manifestations of a common underlying reality, so that to every member of one order there corresponds a determinate member of the other. The two are thus everywhere inseparable and everywhere irreducible “parallel” expressions of a nature which is neither mental nor physical. On this fundamental point our theory, as will have been seen already, completely parts company with Spinozism. That the nature of one and the same common whole should be _equally_ manifested in two entirely irreducible forms, is a patent impossibility. Either the unity of the whole or the absolute disparateness of its twin manifestations must be surrendered if we are to think consistently. Hence we cannot avoid asking in which of the two series the assumed common nature is more adequately expressed. According as we answer this question we shall find ourselves led in the end either to thorough-going Materialism or to thorough-going Idealism. For our own part, the perception that Reality is experience and nothing else has already committed us to the view that both of the seemingly disparate series must in the end be mental. Thus our doctrine may be said to be much what Spinoza’s would be if the attribute of “extension” were removed from his scheme, and the whole of Reality identified with the “infinite intellect of God.”[65] _Consult further_:—B. Bosanquet, _Essentials of Logic_, lect. 2; _Logic_, vol. ii. chap. 7; F. H. Bradley, _Appearance and Reality_, chaps. 13, 14, 20; L. T. Hobhouse, _Theory of Knowledge_, pt. 3, chap. 6, “Reality as a System”; H. Lotze, _Metaphysic_, bk. i. chap. 6 (Eng. trans., vol. i. pp. 163-191); J. S. Mackenzie, _Outlines of Metaphysic_, bk. i. chaps. 2, 3; bk. iii. chap. 6; J. E. M‘Taggart, _Studies in Hegelian Cosmology_, chap. 2. ----- Footnote 54: This consideration obviously influenced Leibnitz. It is a much-decried doctrine in his system that every “monad,” or simple real thing, perceives nothing but its own internal states; there are no “windows” through which one monad can behold the states of another. It is easy to show that this doctrine leads to extremely far-fetched and fantastic hypotheses to account for the apparent communication between different monads, but not so easy to show that Pluralism can afford to dispense with it. See in particular Leibnitz’s _New System of the Nature of Substances_ (Works, ed. Erdmann, 124 ff.; ed. Gerhardt, iv. 477 ff.; Eng. trans. in Latta’s _Leibnis: the Monadology_, etc., p. 297 ff.), especially §§ 13-17 and _Monadology_, §§ 7-9, 51. Footnote 55: