Descartes had already accomplished a great simplification of the speculative problem by summing up all existence under the two heads of extension and thought. It remained to account for these, and to reduce them to a single idea. As we have seen, they were derived from Greek philosophy, and the bond which was to unite them must be sought for in the same direction. It will be remembered that the systems of Plato and Aristotle were bounded at either extremity by a determinate and by an indeterminate principle. With the one, existence ranged between the Idea of Good at the upper end of the scale and empty space at the lower; with the other, between absolute Thought and First Matter. It was by combining the two definite terms, space and thought, that Descartes had constructed his system; and after subtracting these the two indefinite terms remained. In one respect they were even more opposed to each other than were the terms with which they had been respectively associated. The Idea of Good represented unity, identity, and constancy, as against plurality, difference, and change; while Aristotle’s Matter was, by its very definition, multiform, fluctuating, and indeterminate. Nevertheless, there were equally important analogies traceable between them. No very clear account could be given of either, and both were customarily described by negatives. If Matter fell short of complete existence, the Good transcended all existence. If the one was a universal capacity for assuming Forms, the other was the source whence all Forms proceeded. When the distinctive characteristics of an individual were thought away, the question might well be mooted into which principle it would return. The ambiguous use of the word Power contributed still further to their identification, for it was not less applicable to the receptive than to the productive faculty. Now we have just seen into what importance the idea of Power suddenly sprang at the Renaissance: with Bruno it was the only abiding reality of Nature; with Hobbes it was the only object of human desire.
Another term occupying a very large place in Aristotle’s philosophy was well adapted to mediate between and eventually to unite the two speculative extremes. This was Substance; in logic the subject of predication, in metaphysics the substratum of qualities, the οὐσία or Being of the Ten Categories. Now First Matter might fairly claim the position of a universal subject or substance, since it was invested with every sensible quality in turn, and even, as the common element of all Forms, with every thinkable quality as well. Aristotle himself had finally pronounced for the individual compound of Form and Matter as the true substance. Yet he also speaks as if the essential definition of a thing constituted the thing itself; in which case Form alone could be the true subject; and a similar claim might be put forward on behalf of the Plotinian One.[561]
Such were the à priori elements which a historical synthesis had prepared to satisfy the want of a metaphysical Absolute. Let us now see what result would follow when the newly-recovered idea of space was subjected to a metaphysical analysis. Extension is both one and infinite. No particular area can be conceived apart from the whole which both contains and explains it. Again, extension is absolutely homogeneous; to whatever distance we may travel in imagination there will still be the same repetition of similar parts. But space, with the Cartesians, meant more than a simple juxtaposition of parts; having been made the essence of matter, it was invested with mechanical as well as with geometrical properties. The bodies into which it resolved itself were conceived as moving, and as communicating their movement to one another through an unbroken chain of causation in which each constituted a single link, determining and determined by the rest; so that, here also, each part was explained by reference to an infinite whole, reproducing its essence, while exempt from the condition of circumscribed existence. We can understand, then, that when the necessity of accounting for extension itself once became felt, the natural solution would be to conceive it as holding the same relation to some greater whole which its own subdivisions held to their sum total; in other words it should be at once a part, an emanation, and an image of the ultimate reality. This is, in fact, very nearly the relation which Matter holds to the One in the Neo-Platonic system. And we know that with Plotinus Matter is almost the same as infinite Extension.
Corresponding to the universal space which contains all particular spaces, there was, in the Neo-Platonic system, a universal Thought which contained all particular thoughts,—the Nous about which we heard so much in studying Plotinus. Such a conception is utterly strange to the modern mind, but it was familiar enough to Spinoza; and we can see how it would be suggested by the common forms of reasoning. The tendency of syllogism is either to subsume lower under higher notions until a summum genus is reached, or to resolve all subjects into a single predicate, or to connect all predicates with a single subject. The analogies of space, too, would tell in the same direction, bringing nearer the idea of a vast thought-sea in which all particular thoughts, or what to a Cartesian meant the same thing, all particular minds, were contained. And Neo-Platonism showed how this universal Mind or Thought could, like the space which it so much resembled, be interpreted as the product of a still higher principle. To complete the parallelism, it remained to show that Thought, which before had seemed essentially finite, is, on the contrary, co-infinite with Extension. How this was done will appear a little further on.
Spinoza gathered up all the threads of speculation thus made ready for his grasp, when he defined God as a substance consisting of infinite attributes, each of which expresses his infinite and eternal essence; subsequently adding that the essence here spoken of is Power, and that two of the infinite attributes are Extension and Thought, whereof the particular things known to us are modes. Platonism had decomposed the world into two ideal principles, and had re-created it by combining them over again in various proportions, but they were not entirely reabsorbed and worked up into the concrete reality which resulted from their union; they were, so to speak, knotted together, but the ends continued to hang loose. Above and below the finite sphere of existence there remained as an unemployed surplus the infinite causal energy of the One and the infinite passive potentiality of Matter. Spinoza combined and identified the two opposing elements in the notion of a single substance as infinite in actuality as they had been in power. He thus gave its highest metaphysical expression to that common tendency which we traced through the prospects opened out by the Copernican astronomy, the revival of Atomism, the dynamical psychology of Hobbes, and the illimitable passion of the Renaissance, while, at the same time, preserving the unity of Plato’s idealism, and even making it more concentrated than before.
It has been shown how universal space and universal thought at once contain and explain each particular space and each particular concept. In like manner, the infinite substance contains and explains space and thought themselves. Contains them, yes, as attributes; but explains them, how? As two among an infinity of attributes. In other words, if we ask why there should be such an existence as space, the answer is because existence, being infinite, must necessarily include every conceivable thing. The argument is strikingly like a principle of the Epicurean philosophy, and may well have been suggested by it. According to Lucretius, the appearance of design in our world need not be attributed to creative intelligence, because infinite atoms moving in infinite manners through infinite time, must at length arrive, after a comprehensive series of experiments, at the present frame of things;[562] and the same principle is invoked on a smaller scale to account for the origin of organised beings, of memory, and of civil society.[563] In both systems, infinite space is the root-conception; but what Lucretius had legitimately used to explain becoming, Spinoza illegitimately applies to the elucidation of being. At one stroke all empirical knowledge is placed on an à priori foundation. By assuming unlimited credit at the bank of the universe we entitle ourselves to draw a cheque for any particular amount. Thus the idea of infinite attributes is no mere collateral speculation, but forms an essential element of Spinozism. The known varieties of existence are, so to speak, surrounded, supported, and fixed in their places by the endless multitude of the unknown. And this conception of being as absolutely infinite, is another proof of Spinoza’s Platonic tendencies, for it involves the realisation of an abstract idea, that is to say, of Being, which the philosopher treats as something more comprehensive than the facts of consciousness whence it is derived.
Or, again, we may say that two principles,—the Nominalistic as well as the Realistic,—are here at work. By virtue of the one, Spinoza makes Being something beyond and above the facts of experience. By virtue of the other he reinvests it with concrete reality, but a reality altogether transcending our powers of imagination. Very much, also, that Plotinus says about his One might be applied to Spinoza’s Substance, but with a new and positive meaning. The First Cause is above existence, but only existence as restricted within the very narrow limits of our experience, and only as infinite reality transcends the parts which it includes.
It is well known that Spinoza draws a sharp line of demarcation between the two attributes of Extension and Thought, which, with him, correspond to what are usually called body and mind. Neither attribute can act on the other. Mind receives no impressions from body, nor does body receive any impulses from mind. This proposition follows by rigorous logical necessity from the Platonic principle that mind is independent of body, combined with the Stoic principle that nothing but body can act on body, generalised into the wider principle that interaction implies homogeneity of nature. According to some critics, Spinoza’s teaching on this point constitutes a fatal flaw in his philosophy. How, it is asked, can we know that there is any such thing as body (or extension) if body cannot be perceived,—for perceived it certainly cannot be without acting on our minds? The idea of infinite substance suggests a way out of the difficulty. ‘I find in myself,’ Spinoza might say, ‘the idea of extension. In fact, my mind is nothing but the idea of extension, or the idea of that idea, and so on through as many self-reflections as you please. At the same time, mind, or thought, is not itself extended. Descartes and the Platonists before him have proved thus much. Consequently I can conceive extension as existing independently of myself, and, more generally, of all thought. But how can I be sure that it actually does so exist? In this wise. An examination of thought leads me to the notion of something in which it resides—a substance whose attribute it is. But having once conceived such a substance, I cannot limit it to a single attribute, nor to two, nor to any finite number. Limitation implies a boundary, and there can be no boundary assigned to existence, for existence by its very definition includes everything that is. Accordingly, whatever can be conceived, in other words whatever can be thought without involving a contradiction,—an important reservation which I beg you to observe,—must necessarily exist. Now extension involves no contradiction, therefore it exists,—exists, that is to say, as an attribute of the infinite substance. And, by parity of reasoning, there must be an idea of extension; for this also can exist without involving a contradiction, as the simplest introspection suffices to show. You ask me why then I do not believe in gorgons and chimaeras. I answer that since, in point of fact, they do not exist, I presume that their notion involves a contradiction, although my knowledge of natural law is not sufficiently extended to show me where the contradiction lies. But perhaps science will some day be able to point out in every instance of a non-existing thing, where the contradiction lies, no less surely than it can now be pointed out in the case of impossible geometrical figures.’ In short, while other people travel straight from their sensations to an external world, Spinoza travels round to it by the idea of an infinite substance.[564]
The relation of Spinoza’s Substance to its attributes is ambiguous. It is at once their cause, their totality, and their unity. The highly elastic and indefinite term Power helped these various aspects to play into and replace one another according to the requirements of the system. It is associated with the subjective possibility of multiplying imaginary existences to any amount; with the causal energy in which existence originates; and with the expansiveness characteristic alike of Extension and of Thought. For the two known attributes of the universal substance are not simply related to it as co-predicates of a common subject; they severally express its essential Power, and are, to that extent, identical with one another. But when we ask, How do they express Power? the same ambiguity recurs. Substance is revealed through its attributes, as a cause through its effects; as an aggregate through its constituents; and as an abstract notion through its concrete embodiments. Thus Extension and Thought are identical through their very differences, since these illustrate the versatility of their common source, and at the same time jointly contribute to the realisation of its perfection. But, for all practical purposes, Spinoza deals only with the parallelism and resemblance of the attributes. We have to see how he establishes it, and how far he was helped in so doing by the traditions of Greek philosophy.