  Leibniz allied himself with Descartes and most later Cartesians in  opposing material atomism. Nonetheless he was equally concerned to  rebut the Cartesian account of matter according to which the whole  essence of matter is extension – that is, the thesis that  matter is something like geometrical extension made concrete.  Although Leibniz characteristically offers a wide range of arguments  against the Cartesian identification of matter with extension, it  will serve our purposes to focus on three especially  important arguments all rooted in the guiding idea that the notion of extension is simply too impoverished to provide an intelligible  foundation for physics. 