Leibniz was somewhat mean about money. When any young lady at the court of Hanover married, he used to give her what he called a “wedding present,” consisting of useful maxims, ending up with the advice not to give up washing now that she had secured a husband. History does not record whether the brides were grateful.
In Germany Leibniz had been taught a neo-scholastic Aristotelian philosophy, of which he retained something throughout his later life. But in Paris he came to know Cartesianism and the materialism of Gassendi, both of which influenced him; at this time, he said, he abandoned the “trivial schools,” meaning scholasticism. In Paris he came to know Malebranche and Arnauld the Jansenist. The last important influence on his philosophy was that of Spinoza, whom he visited in 1676. He spent a month in frequent discussions with him, and secured part of the Ethics in manuscript. In later years he joined in decrying Spinoza, and minimized his contacts with him, saying he had met him once, and Spinoza had told some good anecdotes about politics.
His connection with the House of Hanover, in whose service he remained for the rest of his life, began in 1673. From 1680 onwards he was their librarian at Wolfenbüttel, and was officially employed in writing the history of Brunswick. He had reached the year 1005 when he died. The work was not published till 1843. Some of his time was spent on a project for the reunion of the Churches, but this proved abortive. He travelled to Italy to obtain evidence that the Dukes of Brunswick were connected with the Este family. But in spite of these services he was left behind at Hanover when George I became king of England, the chief reason being that his quarrel with Newton had
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made England unfriendly to him. However, the Princess of Wales, as he told all his correspondents, sided with him against Newton. In spite of her favour, he died neglected.
Leibniz’s popular philosophy may be found in the Monadology and the Principles of Nature and of Grace, one of which (it is uncertain which) he wrote for Prince Eugene of Savoy, Marlborough’s colleague. The basis of his theological optimism is set forth in the Théodicée, which he wrote for Queen Charlotte of Prussia. I shall begin with the philosophy expounded in these writings, and then proceed to his more solid work which he left unpublished.
Like Descartes and Spinoza, Leibniz based his philosophy on the notion of substance, but he differed radically from them as regards the relation of mind and matter, and as regards the number of substances. Descartes allowed three substances, God and mind and matter; Spinoza admitted God alone. For Descartes, extension is the essence of matter; for Spinoza, both extension and thought are attributes of God. Leibniz held that extension cannot be an attribute of a substance. His reason was that extension involves plurality, and can therefore only belong to an aggregate of substances; each single substance must be unextended. He believed, consequently, in an infinite number of substances, which he called “monads.” Each of these would have some of the properties of a physical point, but only when viewed abstractly; in fact, each monad is a soul. This follows naturally from the rejection of extension as an attribute of substance; the only remaining possible essential attribute seemed to be thought. Thus Leibniz was led to deny the reality of matter, and to substitute an infinite family of souls.
The doctrine that substances cannot interact, which had been developed by Descartes’s followers, was retained by Leibniz, and led to curious consequences. No two monads, he held, can ever have any causal relation to each other; when it seems as if they had, appearances are deceptive. Monads, as he expressed it, are “windowless.” This led to two difficulties: one in dynamics, where bodies seem to affect each other, especially in impact; the other in relation to perception, which seems to be an effect of the perceived object upon the percipient. We will ignore the dynamical difficulty for the present, and consider only the question of perception. Leibniz held that every monad mirrors the universe, not because the universe affects it, but because God has given it a nature which spontaneously produces this result. There is a “pre-
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etablished harmony” between the changes in one monad and those in another, which produces the semblance of interaction. This is obviously an extension of the two clocks, which strike at the same moment because each keeps perfect time. Leibniz has an infinite number of clocks, all arranged by the Creator to strike at the same instant, not because they affect each other, but because each is a perfectly accurate mechanism. To those who thought the pre-established harmony odd, Leibniz pointed out what admirable evidence it afforded of the existence of God.
Monads form a hierarchy, in which some are superior to others in the clearness and distinctness with which they mirror the universe. In all there is some degree of confusion in perception, but the amount of confusion varies according to the dignity of the monad concerned. A human body is entirely composed of monads, each of which is a soul, and each of which is immortal, but there is one dominant monad which is what is called the soul of the man of whose body it forms part. This monad is dominant, not only in the sense of having clearer perceptions than the others, but also in another sense. The changes in a human body (in ordinary circumstances) happen for the sake of the dominant monad: when my arm moves, the purpose served by the movement is in the dominant monad, i.e., my mind, not in the monads that compose my arm. This is the truth of what appears to common sense as the control of my will over my arm.
Space, as it appears to the senses, and as it is assumed in physics, is not real, but it has a real counterpart, namely the arrangement of the monads in a three-dimensional order according to the point of view from which they mirror the world. Each monad sees the world in a certain perspective peculiar to itself; in this sense we can speak, somewhat loosely, of the monad as having a spatial position.
Allowing ourselves this way of speaking, we can say that there is no such thing as a vacuum; every possible point of view is filled by one actual monad, and by only one. No two monads are exactly alike; this is Leibniz’s principle of the “identity of indiscernibles.”
In contrasting himself with Spinoza, Leibniz made much of the free will allowed in his system. He had a “principle of sufficient reason,” according to which nothing happens without a reason; but when we are concerned with free agents, the reasons for their actions “incline without necessitating.” What a human being does always has a motive,
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but the sufficient reason of his action has no logical necessity. So, at least, Leibniz says when he is writing popularly, but, as we shall see, he had another doctrine which he kept to himself after finding that Arnauld thought it shocking.
God’s actions have the same kind of freedom. He always acts for the best, but He is not under any logical compulsion to do so. Leibniz agrees with Thomas Aquinas that God cannot act contrary to the laws of logic, but He can decree whatever is logically possible, and this leaves Him a great latitude of choice.
Leibniz brought into their final form the metaphysical proofs of God’s existence. These had a long history; they begin with Aristotle, or even with Plato; they were formalized by the scholastics, and one of them, the ontological argument, was invented by Saint Anselm. This argument, though rejected by Saint Thomas, was revived by Descartes. Leibniz, whose logical skill was supreme, stated the arguments better than they had ever been stated before. That is my reason for examining them in connection with him.
Before examining the arguments in detail, it is as well to realize that modern theologians no longer rely upon them. Medieval theology is derivative from the Greek intellect. The God of the Old Testament is a God of power, the God of the New Testament is also a God of love; but the God of the theologians, from Aristotle to Calvin, is one whose appeal is intellectual: His existence solves certain puzzles which otherwise would create argumentative difficulties in the understanding of the universe. This Deity who appears at the end of a piece of reasoning, like the proof of a proposition in geometry, did not satisfy Rousseau, who reverted to a conception of God more akin to that of the Gospels. In the main, modern theologians, especially such as are Protestant, have followed Rousseau in this respect. The philosophers have been more conservative; in Hegel, Lotze, and Bradley arguments of the metaphysical sort persist, in spite of the fact that Kant professed to have demolished such arguments once for all.
Leibniz’s arguments for the existence of God are four in number; they are (1) the ontological argument, (2) the cosmological argument, (3) the argument from the eternal truths, (4) the argument from the pre-established harmony, which may be generalized into the argument from design, or the physico-theological argument, as Kant calls it. We will
