Since that which is capable is capable of something and at some time and in some way with all the other qualifications which must be present in the definition and since some things can work according to a rational formula and their potentialities involve a formula, while other things are non rational and their potentialities are non rational, and the former potentialities must be in a living thing, while the latter can be both in the living and in the lifeless; as regards potentialities of the latter kind, when the agent and the patient meet in the way appropriate to the potentiality in question, the one must act and the other be acted on,