 Like many of his contemporaries (e.g., Galileo and Gassendi), Descartes devised his mechanical theory in large part to refute the widely held Aristotelian-based Scholastic explanation of natural phenomena that employed an ontology of “substantial forms” and “primary matter”. Briefly, Scholastic natural philosophy viewed a material body as comprising both an inert property-less substratum (primary matter) and a quality-bearing essence (substantial form), with the latter providing the body’s causal capacities. A quantity of matter, for example, possesses weight, color, texture, and all of the other bodily properties, only in virtue of being conjoined with a determinate form (of a billiard ball, chair, etc.). Descartes admits that he had earlier held such a view of gravity, envisioning the substantial form as a kind of goal-directed (teleological) mental property of bodies: “what makes it especially clear that my idea of gravity was taken largely from the idea I had of the mind is the fact that I thought that gravity carried bodies towards the centre of the earth as if it had some knowledge of the centre within itself. For this surely could not happen without knowledge, and there can be any knowledge except in a mind” (AT VII 442). In a revealing passage from The World, Descartes declares the Scholastic hypothesis to be both an unintelligible and inadequate methodological approach to explaining natural phenomena: