 Leibniz’s metaphysics was developed within, and in part as a reaction to the mechanical philosophy of the mid-to-late 17th century, revived by Galileo, Descartes, Gassendi, Boyle, Newton, and Locke. While the term “substance,” meaning the indestructible stuff of the universe, was retained by Descartes in his discussions of res extensa, the mechanical philosophers adopted a corpuscularian theory in which objects were temporary aggregates of solid, indestructible particles with various figures and motions, and most though by no means all change occurred through their contact, pressure, collision, entangling, and so on. Leibniz contested the corpuscularian image, insisting that it was insufficiently profound and inherently self-contradictory (G 4: 480), and holding that matter was a ‘phenomenon’ founded upon the reality of “metaphysical points” or, as he later termed them, monads: qualitatively unique,indestructible and indivisible units that also perceived and strove (G 6: 608).