That act is within the idea of being is assumed since to actually be is to actually be. Potency, though, is also contained within the concept of being. The possible as possible is contrary to the impossible. That which cannot come to be or become is impossible to be. Non-being is that which cannot come to be or become. and so is impossible to be, therefore being, since it is contrary to non-being, is also contrary to impossibility to be. Therefore being includes within itself the concept of the possible. To distinguish what is and what is possible is nothing other than to distinguish act from potency.