 The existence of matter endowed with forms in an inchoate state is necessary, according to Kilwardby, in order to distinguish generation from creation as well as to assure that generation is a natural (and not violent) change—since an active potency is an internal principle of motion. Another of the applications of the notion of active potency is to explain elemental change. Every part of PPM that is informed by the form of a body has the forms of all four elements in potency. At any given time, only one of these forms can be actual. The elements transmute into one another in virtue of their active and passive qualities (DOS 249). With this account, Kilwardby addresses the question of the presence of the four elements’ forms existing within mixed bodies differently from other authors of his time. He takes his notion of potency, being a form in an inchoate state of actuality, as sufficient to avoid the problem of the simultaneous, fully actual presence of contraries in one and the same subject.