Aristotle is absolute in stating “Every craft and every investigation, and likewise every action and decision, seems to aim at some good; hence the good has been well described as that at which everything aims” (1094a). However, this does not mean that everything aims at the same ‘goods’. As he says, “there is an apparent difference among the ends aimed at” (1094a). Whereas humanity shares the characteristics of plant and animal life, and whereas the same things which are good for the wellbeing of plants and animals are also good for us (nourishment, health, etc) the good at which we aim is different and greater than the good at which a plant, for example, aims in growing and reproducing. This is because of the specific difference between humans and other living things, plant or animal.
What makes humans unique? What is our function that differentiates our good from other goods? “The human function is the soul’s activity that expresses reason, or requires reason” (1098a5). This expression and requirement of reason is for the human “a certain kind of life” which when completed well expresses “proper virtue” (1098a10). As this is regarded as the right function of the human being, the virtue of living well according to reason is the human good. “The human good turns out to be the soul’s activity that expresses virtue” (1098a15).
Aristotle backs up this deductive argument with inductive observation. People manifestly want to be happy. There are different goods which people associate with happiness: external goods, goods of the soul, and goods of the body (1098b10). Goods of the soul are considered to be goods to the fullest extent and most of all, because external goods and goods of the body are fleeting, transitory, and subject to sudden changes in fortune. Also, oxes or horses, may possess external goods (food) and goods of the body (health) but they are not regarded as being happy, as the goods of the soul include the rational awareness of one’s situation and conduct in life. “Happiness is an activity of the [rational] soul” (1100a15). And of all the activities that the human may do, practicing the virtues is the greatest, as the virtues alone are “pleasant in themselves” (1090a20). Also, they contribute to “the state that makes a human being good and makes him perform his function [rationality] well.” (1106a20).