This potency is not an active power. Power to effect something to work, at least when understood as active, is the absolute contrary of the power or potency with which we are now concerned, because it is not really potency but act. The potency of which we are speaking is entirely passive, nothing more than a real power of being or becoming. Wax is in potency to receive the impress of the seal, water in potency to become ice or vapour. ACT Since, however, power of being, though not nothing, is not being in the full and primary sense of the term, we must find a name for being in the full and primary sense of the term as distinguished from potentiality.
Philosophers call it act.
Here also we must be aware of ambiguity. We are not concerned, at least not primarily and chiefly, with an act , in the ordinary sense of the word, with doing or action . Action presupposes being. For example, a body is luminous in act, even when it is not illuminating anything else. Fahrenheit is ice in act , and the moment anything effectively is one thing or another and especially the moment any thing exists, it is in act.