Considerations sur la doctrine d'un esprit universel (1702). Opera, ed. Dutens, II. ii. zo.
content of each monad is in "accord" or correspondence with that of every other (cf. p. 127), though this content is represented with infinitely varying degrees of perfection. This is Leibnitz's famous doctrine of pre-established harmony, in virtue of which the infinitely numerous independent substances of which the world is composed are related to each other and form one uni verse. It is essential to notice that it proceeds from the very nature of the monads as percipient, self-acting beings, and not from an arbitrary determination of the Deity. From this harmony of self-determining percipient units Leibnitz has to explain the world of nature and mind. Space and time are merely relative, the former an order of coexistences, the latter of successions (pp. 682, 752). Hence not only the secondary qualities of Descartes and Locke, but their so-called primary qualities as well, are merely phenomenal (p. 445). The monads are really without position or distance from each other; but, as we perceive several simple substances, there is for us an aggregate or extended mass. Body is thus active extension (pp. hio, III). The unity of the aggre gate depends entirely on our perceiving the monads composing it together. There is no such thing as an absolute vacuum or empty space, any more than there are indivisible material units or atoms from which all things are built up (pp. 126, 186, 277).
From Leibnitz's doctrine of force as the ultimate reality it fol lows that his view of nature must be throughout dynamical. And though his project of a dynamic, or theory of natural philosophy, was never carried out, the outlines of his own theory and his criticism of the mechanical physics of Descartes are known to us. The whole distinction between the two lies in the difference be tween the mechanical and dynamical views of nature. Descartes's principle is now enunciated as the conservation of momentum, that of Leibnitz as the conservation of energy Like the monad, body, which is its analogue, has a passive and an active ele ment. The former is the capacity of resistance, and includes impenetrability and inertia; the latter is active force (pp. 25o, 687). Bodies, too, like the monads, are self-contained activities, receiving no impulse from without—it is only by an accommoda tion to ordinary language that we speak of them as doing so—but moving themselves in harmony with each other (p. 25o).
these essays he worked out a theory of the origin and develop ment of knowledge in harmony with his metaphysical views, and thus without Locke's implied assumption of the mutual influence of soul and body. When one monad in an aggregate perceives the others so clearly that they are in comparison with it bare monads (monades noes), it is said to be the ruling monad of the aggre gate, not because it actually does exert an influence over the rest, but because, being in close correspondence with them, and yet having so much clearer perception, it seems to do so (p. 683). This monad is called the entelechy or soul of the aggregate or body, and as such mirrors the aggregate in the first place and the universe through it (p. 0). Each soul or entelechy is surrounded by an infinite number of monads forming its body (p. 714); soul and body together make a living being, and, as their laws are in perfect harmony—a harmony established between the whole realm of final causes and that of efficient causes (p. 714)—we have the same result as if one influenced the other. Thus the body does not act on the soul in the production of cognition, nor the soul on the body in the production of motion. The body acts just as if it had no soul, the soul as if it had no body (p. 711). Instead, therefore, of all knowledge coming to us directly or indirectly through the bodily senses, it is all developed by the soul's own activity, and sensuous perception is itself but a confused kind of thought. Not a certain select class of our ideas only (as Des cartes held), but all our ideas, are innate, though only worked up into actual thought in the development of knowledge (p. 212). To the aphorism made use of by Locke, "Nihil est in intellectu quod non prius fuerit in sensu," must be added the clause, "nisi intellectus ipse" (p. 223). The soul at birth is not comparable to a tabula rasa, but rather to an unworked block of marble, the hidden veins of which already determine the form it is to assume in the hands of the sculptor (p. 196). Nor, again, can the soul ever be without perception; for it has no other nature than that of a percipient active being (p. 246). Apparently dreamless sleep is to be accounted for by unconscious perception (p. 223) ; and it is by such unconscious perceptions that Leibnitz explains his doctrine of pre-established harmony (p. 197).