Matter, mind and human life
The details of Leibniz’s account of matter and its relation to mind are obscure and much debated, but I think we can make sense of the general position.1 Consider for example an individual material thing, like a tree. Nowadays we tend to assume that the most accurate description of the tree, the one which tells us what it is really like in itself, is a materialistic one which represents the tree as a collection of atoms which are themselves made up of smaller, subatomic parts. Leibniz, like Descartes and Spinoza,
thinks any such account is obviously wrong: no atomistic account can ever provide an explanation of matter, because if the most fundamental subatomic particles are still material objects, then however small they are they have some determinate size, and so are not ultimate, but built up out of something smaller, and so on ad infinitum. And if the smallest particles are not themselves material objects, then atomism is not in fact a materialistic account after all, and we need some explanation of what those particles are, and how matter arises from them (cf. p. 271, footnote 6).