Precisely so far as things can be something they are not, they, after an inferior fashion, are. This inferior mode of being is called, by Aristotle, potency or potentiality. Aristotle calls it actuality, or act. We must be careful not to attempt to think with our imagination this concept of potentiality. It can be thought by the intellect alone.
Potentiality is, in itself, absolutely incapable of being represented.
It is absolutely nothing done or in th e process of doing, absolutely nothing in act. In itself it cannot be conceived for in that case it would necessarily be conceived as something determinate. It can be conceived only by means of the act to which it is ordered. How did Aristotle arrive at this idea of the reality of the potential. But for one bein g to become another being, it must both actually be what it is, and have the real potentiality to become other that what it is.