 Alongside matter, the other internal principle of composite substances is form, and so form too counts as a substance (LongAnima II.2), and indeed is substance in the most proper sense of the term (Amerini 2008; Di Giovanni 2012). Substantial forms can be distinguished from accidents in that a subject (a dog, a stone) endures through the gain and loss of its accidents, whereas when the substantial form of the subject departs, the subject ceases to exist or exists only homonymously (ParaAnima 2.120)—as one might speak of cremating one’s grandfather. Interpreters have disagreed on whether Ibn Rushd allows a single substance to have multiple substantial forms. But at least sometimes he seems to suppose that one substance has just one form, as when he holds that “if prime matter were to have its own form, it would receive no other form, while enduring, but would immediately be corrupted as soon as that other form were generated” (LongPhys I.69; see SubstOrb 1.50). If elsewhere he seems to suggest that any necessary feature of a thing will count as a substantial form of it, this may mean merely that a substantial form is a composite of multiple discrete, incomplete constituents (Di Giovanni 2011; Cerami 2015, 521–4). Ibn Rushd is clear, at any rate, that the essence (dhāt) or quiddity (māhiyya) of a thing is accounted for entirely by its form, rather than by its form and matter (LongMeta VII.34 {896}). Thus, “form is the primary substance only because it is the cause of the determinate substance and the determinate substances come to be substance only by it” (LongMeta VII.5 {761k}).