and of activity. He presents a unity in which all distinction of individuals is lost, and in which there is no room for change. But Spinoza certainly presented the problem more clearly to Leibniz, and revealed more definitely the conditions of its solution. The search is henceforth for a unity which shall avoid the irresolvable dualism of Descartes, and yet shall allow free play to the principles of individuality and of activity. There must be, in short, a universe to which the individual bears a real yet independent relation. What is this unity? The answer, in the phraseology of Leibniz, is the monad. Spinoza would be right, said Leibniz, were it not for the existence of monads. I know there are some who have done Leibniz the honor of supposing that this is his way of saying, “Spinoza is wrong because I am right;” but I cannot help thinking that the saying has a somewhat deeper meaning. What, then, is the nature of the monad? The answer to this question takes us back to the point where the discussion of the question was left at the end of chapter second. The nature of the monad is life. The monad is the spiritual activity which lives in absolute harmony with an infinite number of other monads.
Let us first consider the reasons of Leibniz for conceiving the principle of unity as spiritual. Primarily it is because it is impossible to conceive of a unity which is material. In the sensible world there is no unity. There are, indeed, aggregations, collections, which seem like unities; but the very fact that these are aggregations shows that the unity is factitious. It is the very nature of matter to be infinitely divisible: to say this is to deny the existence of any true principle of unity. The world of nature is the world of space and time; and where in space or time shall we find a unity where we may rest? Every point in space, every moment in time, points beyond itself. It refers to a totality of which it is but a part, or, rather, a limitation. If we add resistance, we are not better situated. We have to think of something which resists; and to this something we must attribute extension,—that is to say, difference, plurality. Nor can we find any resistance which is absolute and final. There may be a body which is undivided, and which resists all energy now acting upon it; but we cannot frame an intelligible idea of a body which is absolutely indivisible. To do so is to think of a body out of all relation to existing forces, something absolutely isolated; while the forces of nature are always relative to one another. That which resists does so in comparison with some opposing energy. The absolutely indivisible, on the other hand, would be that which could not be brought into comparison with other forces; it would not have any of the attributes of force as we know it. In a word, whatever exists in nature is relative in space, in time, and in qualities to all else. It is made what it is by virtue of the totality of its relations to the universe; it has no ultimate principle of self-subsistent unity in it.
Nor do we fare better if we attempt to find unity in the world of nature as a whole. Nature has its existence as a whole in space and time. Indeed, it is only a way of expressing the totality of phenomena of space and time. It is a mere aggregate, a collection. Its very essence is plurality, difference. It is divisible without limit, and each of its divisions has as good a right to be called one as the whole from which it is broken off. We shall consider hereafter Leibniz’s idea of infinity; but it is easy to see that he must deny any true infinity to nature. An ultimate whole made up of parts is a contradictory conception; and the idea of a quantitative infinite is equally so. Quantity means number, measure, limitation. We may not be able to assign number to the totality of occurrences in nature, nor to measure her every event. This shows that nature is indefinitely greater than any assignable quantity; but it does not remove her from the category of quantity. As long as the world is conceived as that existing in space and time, it is conceived as that which has to be measured. As we saw in the last chapter, the heart of the mechanical theory of the world is in the application of mathematics to it. Since quantity and mathematics are correlative terms, the natural world cannot be conceived as infinite or as an ultimate unity.
In short, Leibniz urges and suggests in one form and another those objections to the mechanical theory of reality which later German philosophers have made us so familiar with. The objections are indeed varied in statement, but they all come to the impossibility of finding any unity, any wholeness, anything except plurality and partiality in that which is externally conditioned,—as everything is in nature.
But the reasons as thus stated are rather negative than positive. They show why the ultimate unity cannot be conceived as material, rather than why it must be conceived as spiritual. The immediate evidence of its spiritual nature Leibniz finds in the perception of the one unity directly known to us,—the “me,” the conscious principle within, which reveals itself as an active force, and as truly one, since not a spatial or temporal existence. And this evidence he finds confirmed by the fact that whatever unity material phenomena appear to have comes to them through their perception by the soul. Whatever the mind grasps in one act, is manifested as one.
But it is not in any immediate certainty of fact that Leibniz finds the best or completest demonstration of the spiritual nature of the ultimate unity. This is found in the use which can be made of the hypothesis. The truest witness to the spiritual character of reality is found in the capacity of this principle to comprehend and explain the facts of experience. With this conception the reason of things can be ascertained, and light introduced into what were otherwise a confused obscurity. And, indeed, this is the only sufficient proof of any doctrine. It is not what comes before the formulation of a theory which proves it; it is not the facts which suggest it, or the processes which lead up to it: it is what comes after the formation of the theory,—the uses that it can be put to; the facts which it will render significant. The whole philosophy of Leibniz in its simplicity, width, and depth, is the real evidence of the truth of his philosophical principle.
The monad, then, is a spiritual unity; it is individualized life. Unity, activity, individuality are synonymous terms in the vocabulary of Leibniz. Every unity is a true substance, containing within itself the source and law of its own activity. It is that which is internally determined to action. It is to be conceived after the analogy of the soul. It is an indivisible unity, like “that particular something in us which thinks, apperceives and wills, and distinguishes us in a way of its own from whatever else thinks and wills.” Against Descartes, therefore, Leibniz stands for the principle of unity; against Spinoza, he upholds the doctrine of individuality, of diversity, of multiplicity. And the latter principle is as important in his thought as the former. Indeed, they are inseparable. The individual is the true unity. There is an infinite number of these individuals, each distinct from every other. The law of specification, of distinction, runs through the universe. Two beings cannot be alike. They are not individualized merely by their different positions in space or time; duration and extension, on the contrary, are, as we have seen, principles of relativity, of connection. Monads are specified by an internal principle. Their distinct individuality is constituted by their distinct law of activity. Leibniz will not have a philosophy of abstract unity, representing the universe as simple only, he will have a philosophy equal to the diversity, the manifold wealth of variety, in the universe. This is only to say that he will be faithful to his fundamental notion,—that of Life. Life does not mean a simple unity like a mathematical one, it means a unity which is the harmony of the interplay of diverse organs, each following its own law and having its own function. When Leibniz says, God willed to have more monads rather than fewer, the expression is indeed one of naïveté, but the thought is one of unexplored depth. It is the thought that Leibniz repeats when he says, “Those who would reduce all things to modifications of one universal substance do not have sufficient regard to the order, the harmony of reality.” Leibniz applies here, as everywhere, the principle of continuity, which is unity in and through diversity, not the principle of bare oneness. There is a kingdom of monads, a realm truly infinite, composed of individual unities or activities in an absolute continuity. Leibniz was one of the first, if not the first, to use just the expression “uniformity of nature;” but even here he explains that it means “uniform in variety, one in principle, but varied in manifestation.” The world is to be as rich as possible. This is simply to say that distinct individuality as well as ultimate unity is a law of reality.
But has not Leibniz fallen into a perilous position? In avoiding the monotone of unity which characterizes the thought of Spinoza, has he not fallen into a lawless variety of multiplicity,
