Can a bridge be constructed between Whiteheadian process metaphysics and Aristotelian-Scholastic substance metaphysics? I ask this question in the context of physical change, using the chemical transformation of molecules as the quintessential exemplar. While both metaphysical systems describe nature as dynamical and relational, each sees change differently: for process metaphysics, change is constitutive of all actualities, while for substance metaphysics, change is secondary and something that happens to actualities. My analysis concludes that these two systems of thought have fundamental metaphysical (...) differences that do not permit a reconciliation. Rather than reconciliation, what might be possible is the development of a new way to speak about the actualities of world, not as substances or processes but a way that subsumes both. (shrink)