MIND AND SOUL understanding of substance’ (G IV.469) It was for this reason that the notion of substantial form had to be rehabilitated Once the role of force was appreciated, it was matter, not form, that turned out to be illusory Cartesian extension was a pure phenomenon, he told Arnauld, like a rainbow.7 Leibniz was, however, still trapped in Descartes’ false dichotomy of mind and matter Because force could Wnd no place in a world of mere extension, he located it in the realm of the mental He thought of it as a form of appetition analogous to human desire and volition This comes out most clearly in the mature form of his philosophy presented in his Monadology The monads or entelechies which are the basis of his system have the properties only of mind The inert bodies that we see and feel around us are only phenomena, aggregates of invisible, intangible monads They are not illusory entities—they are, in Leibniz’s phrase, well-founded phenomena But the only true substances are the monads Monads are independent, indivisible, and unrepeatable Having no parts, they cannot grow or decay; they can only be created or annihilated They can change, but only in the way that souls can change As they have no physical properties to alter, their changes must be changes of mental states The life of a monad, Leibniz tells us, is a series of perceptions A perception is an internal state that is a representation of other items in the universe This inner state will change as the environment changes, not because of the environmental change, but because of the internal drive or ‘appetition’ that has been programmed into them by God Monads are incorporeal automata; they are everywhere and there are countless millions of them: There is a world of created beings—living things, animals, entelechies and souls— in the least part of matter Each portion of matter may be conceived as a garden full of plants and as a pond full of Wsh But every branch of each plant, every member of each animal, and every drop of their liquid parts is itself likewise a similar garden or pond (G VI.66 ) The idea that the human body is an assemblage of cells, each living an individual life, was still a new one, though not of course peculiar to Leibniz Here I am indebted to Daniel Garber, ‘Leibniz on Body, Matter, and Extension’, PASS (2004): 23–40 233