Aristotle believed that God exists necessarily, which means that God does not depend on anything else for existence. He never changes or has any potential to change, never begins and never ends and so is eternal. Eternal things, Aristotle claimed must be good; there can be no defect in something that exists necessarily, because evil is connected with some kind of lack, a not-being of something which ought to be there, an absence of the “actuality” that Aristotle thought God most perfectly has!