Bacon, Descartes, and Spinoza, disagreeing widely on other subjects, were agreed in discountenancing the study of final causes: Bacon, apparently, from dislike of the idea that the perfect adaptation of all things to the service of man rendered superfluous any efforts to make them more serviceable still; Descartes from his devotion to the mathematical method which was more applicable to a system of mechanical causation; Spinoza for the same reason, and also from his disbelief in a personal God. Leibniz, on the contrary, felt deeply impressed by a famous passage in Plato's Phædo, where Socrates, opposing the philosophy of teleology to the philosophy of mechanism, desiderates an explanation of nature as designed with a view to the highest good. But Leibniz did not go so far as Plato. Mediating between the two methods, he taught that all is done for the best, but also that all is done through an unbroken series of efficient causes. At the same time, these causes are only material in appearance; in reality they are spiritual beings. There is no such thing as dead matter; the universe consists of living forces all through. The general idea of force probably came from that infinite Power of which, according to Spinoza, the whole universe is at once the product and the expression; or it may have been suggested by Plato's incidental identification of Being with Action. But Leibniz found his type of force in human personality, which, following the lead of Aristotle
rather than of Plato, he conceived as an Entelechy, or realised Actuality, and a First Substance. After years of anxious reflection he chose the far happier name of Monad, a term originally coined by Bruno, but not, as would appear, directly borrowed from him by the German metaphysician.
According to Leibniz, the monads or ultimate elements of existence are constituted by the two essential properties of psychic life, perception and appetency. In this connection two points have to be made clear. What he calls bare monads—i.e., the components of what is known as inorganic matter—although percipient, are not conscious of their perceptions; in his language they do not apperceive. And he endeavours to prove that such a mentality is possible by a reference to our own experience. We hear the roaring of waves on the seashore, but we do not hear the sound made by the falling of each particle of water. And yet we certainly must perceive it in some way or other, since the total volume of sound is made up of those inaudible impacts. He overlooks the conceivable alternative that the immediate antecedent of our auditory sensations is a cerebral disturbance, and that this must attain a certain volume in order to produce an effect on our consciousness. The other point is that the appetency of a monad does not mean an active impulse, but a search for more and more perceptions, a continuous widening of its cognitive range. In short, each monad is a little Leibniz for ever increasing the sum of its knowledge.
At no stage does that knowledge come from experience. The monad has no windows, no communication of any kind with the external world. But each reflects the whole universe, knowing what it knows by
mere introspection. And each reflects all the others at a different angle, the angles varying from one another by infinitesimal degrees, so that in their totality they form a continuous series of differentiated individuals. And the same law of infinitesimal differentiation is observed by the series of progressive changes through which the monads are ever passing, so that they keep exact step, the continuity of existence being unbroken in the order of succession as in the order of co-existence. Evidently there is no place for free-will in such a system; and that Leibniz, with his relentless fatalism, should not only admit the eternal punishment of predestined sinners, but even defend it as morally appropriate, obliges us to condemn his theology as utterly irrational or utterly insincere.
In this system animal and human souls are conceived as monads of superior rank occupying a central and commanding position among a multitude of inferior monads constituting what we call their bodies, and changing pari passu with them, the correspondence of their respective states being, according to Leibniz, of such a peculiarly intimate character that the phenomena of sensation and volition seem to result from a causal reaction instead of from a mechanical adjustment such as we can imagine to exist between two clocks so constructed and set as to strike the same hour at the same time. This theory of the relations between body and soul is known to philosophy as the system of pre-established harmony.
It may be asked how every monad can possibly reflect every other monad when we do not know what is passing in our own bodies, still less what is passing all over the universe. The answer consists in a convenient distinction between clear and confused
perceptions, the one constituting our actual and the other our potential knowledge. A more difficult problem is to explain how any particular monad—Leibniz or another—can consistently be a monadologist rather than a solipsist believing only in its own existence. Here, as usual, the Deus ex Machina comes in. Following Descartes, I think of God as a perfect Being whose idea involves his existence, with, of course, the power, will, and wisdom to create the best possible world—a universe of monads—which, again, by its perfect mutual adjustments, proves that there is a God. A more serious, and indeed absolutely insuperable, objection arises from the definition of the monads as nothing but mutually reflecting entities. For even an infinity of little mirrors with nothing but each other to reflect must at once collapse into absolute vacuity. And with their disappearance their creator also disappears. God, the supreme monad, we are told, has only clear perceptions; but the clearness is of no avail when he has nothing to perceive but an absolute blank. Leibniz rejected the objectivity of time and space; yet the hollow infinity of those blank forms seems, in his philosophy, to have reached the consciousness of itself.