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. Act may therefore be defined as being in the strict sense of the term, taken in the fullness thus signified, or again the finished, the determinate , or the perfect as such. We must take care not to attempt to think with our imagination these concepts of act and potentiality. They can be thought by the intellect alone.