 The question James faces in Quodl. I, q. 21 is a markedly theological one, namely whether, if the soul were to take on the ashes or the matter of another man at resurrection, the resulting individual would be the same as before resurrection. In order to answer that question, James tells us, it is first necessary to determine what the cause of numerical unity is in the case of composite beings. There have been numerous answers to that question and James provides a short account of each. Some philosophers have appealed to quantity as the principle of numerical unity; others to matter; others yet to matter as subtending indeterminate dimensions; finally, others have turned to form as the cause of individuation. According to James, each of these answers is part of the correct explanation though each is insufficient if taken on its own. The correct view, according to him, is that form and matter taken together are the principal causes of numerical identity in the composite, with quantity contributing something “in a certain manner.” Form and matter, however, are principal causes in different ways; more precisely, each accounts for a different kind of numerical unity. For by ‘singularity’ we can really mean two distinct things: we can mean the mere fact of something’s being this or that singular thing, or we can point to a thing qua “something complete and perfect within a certain species” (Quodl. I, 21, 227, 134–35). It is matter that accounts for the first kind of singularity, and form for the second. Put otherwise, the kind of unity that accrues to a thing on account of its being a mere singular results from the concurrence of the “substantial” unity provided by matter and the “accidental” unity provided by quantity. By contrast, the unity that characterizes a thing by virtue of the perfection or completeness it displays is conferred to it by the form, which is the principle of perfection and actuality in composites.