 Matter exists only when actualized by form, but the first form it receives is not the nature of the composite substance (dog, stone, etc.) but instead the “indeterminate dimensions” (al-abʿād ghayr al-maḥdūdat) that give matter its corporeal character: “the three dimensions that constitute the nature of body are the first state in matter, and matter cannot be devoid of them in any instance of generation: not that they exist in matter in actuality, but rather in some kind of potentiality different from the potentiality in which matter is constituted” (ParaGC I.4.26 {32}; SubstOrb 1.55). In postulating a persisting extended substratum beneath all physical change, Ibn Rushd has been said to take a step toward the res extensa of seventeenth-century mechanical philosophy (Hyman 1965). But his conception of matter, far from making further forms unnecessary, explains how multiple forms can be instantiated in the same material stuff: “the presence of dimension in prime matter is a prerequisite for the existence of contraries” (EpiMeta 3.126 {112}). Since forms, by their nature, are always individuals—universals, Ibn Rushd insists, do not exist outside the soul (EpiMeta 2.73–5 {57–9})—the theory does not require a “principle of individuation” for form. Extended matter does, however, serve as what might be called a principle of multiplication. If the material realm were not extended, “there would exist in it only one form at a given time” (SubstOrb 1.60; Di Giovanni 2007).