 In this passage, Descartes seems to deny the existence of inertial force if conceived as a form of Scholastic quality that material bodies can possess; rather, bodies are “indifferent to motion”, so even the slightest weight should move the entire earth. On the other hand, he is willing to acknowledge the commonly observed fact that larger objects are much harder to set in motion than smaller objects. Consequently, although Descartes finds the existence of “forces of resistance” (or “natural sluggishness”) problematic, as is the case with such similar properties as weight, he does not entirely relegate inertia to the phenomenological status of the so-called secondary properties of matter (such as color, taste, etc., which only exist in the mind). The main reason for this inclusion of inertial force effects into scientific discourse can probably be traced to Descartes’ classification of motion as an intrinsic characteristic or “mode” of extension (see  Section 3).  As the concluding sections of the Principles state: “I have now demonstrated [there] are nothing in the [material] objects other than…certain dispositions of size, figure and motion…” (Pr IV 200). Since inertial forces are a consequence or a by-product of motion, as the product of the size times speed of bodies, Descartes apparently did not object to incorporating these phenomena within the discussion of the modes of material substance.