Aristotle's Purpose Argument

Aristotle's train of thought here runs along tracks laid in his philosophy of nature. All animals, plants and even simple things like the four elements are pursuing some kind of goal. If there is a human function, it must be characteristic of humans. It must be the performance of an activity that belongs to us alone. For it is rationality that distishes us from plants and animals. This is aristotle's so called function argument, which provides the foundation for the rest of his ethics.