 Yet, even if Descartes described force as an intrinsic fact of material interactions, the exact nature of the relationship between force and matter remains rather unclear. In particular, is force a property actually contained or present within bodies? Or, is it some sort of derivative phenomenal effect of the action of speed and size, and thus not present within extension? On the former interpretation (as favored by Alan Gabbey 1980, and Martial Gueroult 1980), forces exist in bodies in at least one important sense as “real” properties or modes whose presence occasions the Cartesian laws of nature. While many of Descartes’ explanations might seem to favor this interpretation (e.g., “[a body] at rest has force to remain at rest”, Pr II 43), Daniel Garber charges that such views run counter to Descartes’ demand that extension alone comprise the essence of matter. Garber suggests that we view Cartesian force as a sort of shorthand description of the dynamical regularities maintained in the world by God, and not as some form of quality internal to bodies: “The forces that enter into the discussion [of the Cartesian collision laws] can be regarded simply as ways of talking about how God acts, resulting in the law-like behavior of bodies; force for proceeding and force of resisting are ways of talking about how, …, God balances the persistence of the state of one body with that of another” (Garber 1992a, 298; see also Hatfield 1979, Des Chene 1996, and Manchak 2009, for more approaches). In various passages associated with the conservation principle, Garber’s interpretation apparently gains credibility. For instance: “So in now maintaining the world by the same action and with the same laws with which He [God] created it, He conserves motion; not always contained in the same parts of matter, but transferred from some parts to others depending on the ways in which they come in contact” (Pr II 42). In retrospect, however, it must be acknowledged that Descartes’ classification of material substance with extension, as exemplified in his demand that there exists nothing in bodies except “certain dispositions of size, figure and motion”, is so open-ended and equivocal as to easily accommodate both of the interpretations surveyed above. All that can be safely concluded is that Descartes envisioned the forces linked with bodily inertial states as basic, possibly primitive, facts of the existence of material bodies—a broad judgment that, by refusing to take sides, opts out of this difficult ontological dispute.