It was mentioned in Chap. 1 that the ontological commitment to the existence of processes is developed in this book alongside the commitment to quantities of matter and individuals without any call on the reduction of continuant matter to occurrents. But precisely this reductionist thesis has been advanced in recent years in the field of biology under the heading of processual philosophy (to distinguish it from the motivation and formulation of an analogous thesis in the wake of Whitehead’s process philosophy). Processual philosophy is primarily motivated by the dynamic state of organisms’ constitutive matter resulting from metabolism, their morphological development and the wholesale interaction of organisms with their environments. It is presented as standing opposed to the traditional doctrine of substance with its commitment to essentialism. Essential traits are held to underly natural classification and to determine what it is for the same thing to continue to exist through time. This chapter presents processual philosophy, principally on the basis of the book Everything Flows edited by Nicholson and Dupré, and upholds the primitive role of continuants by developing an argument countering the reductionist thesis. The argument hinges on the contention—the main theme of Chap. 3 —that individuals, exemplified by biological organisms, are for a given period constituted of a quantity of matter which may well not be fixed over longer and shorter periods of time.