Plato thinks that someone who has a complete grasp of what goodness is, who has made no mistakes respecting what is good, will have an explanation of all actions, both those which really do lead upwards in a heirarchy of goods to enable human perfection, and those which fail due to mistaken notions of what is good. Plato also thinks that not only human actions but everything else that goes on in the universe is aimed towards some good. Aristotle's progress . So he does not suppose that the soul could exist apart from the body, since the way something is organized could not exist when WHAT was organized had disappeared. Aristotle begins his discussion of ethics with some obvious points.
Actions aim at some good.
Some of the goods that are aimed at must be wanted for their own sake, not as a means to something else. Moreoever there must be some highest, or most comprehensive or in some sense complete good. Some say pleasure, some same fame and honor, some say virtue. Aristotle sees problems with all of these, though a version of the third, as it turns out, is about the same as his own view. The problem then is to come up with a viable definition of happiness.