Happiness is the first thing examined in Nicomachean Ethics. Aristotle points out that happiness is the ultimate end of human beings; and, it is complete and self-sufficient. He defines “the good as what everything seeks.” Also, there are different degrees of the good, such as low, high, and highest. To evaluate the degree of the good, Aristotle distinguishes the means and the end. Precisely, the means is that which is done for the sake of the end. And, the end is always better than the means because it is unreasonable to do anything for a thing worse than the means. “Wherever there are ends apart from the actions, the products are by nature better than the activities.” Therefore, the highest good must be done not for any other end but for itself only. Aristotle argues that although the goods such as “honor, pleasure, understanding, and every virtue” may be chosen for themselves, they are also the means to happiness. It is true that insofar as a man attains happiness, he will never desire anything further and he lacks nothing in his life. Therefore, happiness ends in itself and is the highest good.
Having determined happiness as the highest good, Aristotle discusses how happiness can be achieved. Firstly, he criticizes hedonism which takes pleasure as the end. Man is pleased by “the condition of the soul.” However, pleasure does not involve any activity of the soul. Therefore, pleasure is unable to properly please man. In contrast, the life in accord with virtue is the life of the soul. Thus, man of this life is naturally pleased in his action and needs not any extra pleasure. For instance, a man doing a just action is happy because of the action. And, he cannot be called just if he is not pleased by a just action. Secondly, Aristotle disagrees with Socrates’ notion that virtue is sufficient for happiness. He points out the paradox between Socrates’ view and the common beliefs. Particularly, despite the fact that a man lives a life of virtue, a life with the worst evils and misfortunes cannot be called a happy life. Accordingly, a happy life must have external goods of some sorts. In a word, a happy life is a complete life. Lastly, he asserts that “happiness is a certain sort of activity of the soul in accord with virtue.” In brief, virtue makes man happy. And, this happiness does not involve any fortune. Hence, both complete life and complete virtue are necessary to be happy. Nevertheless, if man has to choose between a virtuous act and a fortune incompatible to virtue, it is more reasonable to choose virtue. That is why “someone bears many severe misfortunes with good temper, not because he feels no distress, but because he is noble and magnanimous.”
According to Aristotle, the end of things is the state in which they are fully actualized. To be actualized, things must necessarily follow their natures. Aristotle reuses Plato’s definition of function and attempts to find the true human function which human beings only can do or which they do better than everything else. And, by means of the human function, man is able to achieve the perfection of human nature, happiness. Thus, the human function is characteristic activity in accord with nature to pursue the end. The function cannot belong to the sort of life of nutrition or sense perception because this sort of life is shared with plants and animals. Accordingly, “the human function is activity of the soul in accord with reason and requiring reason.” Furthermore, a function is well completed in accord with a proper virtue since human virtue, the same as Plato’s definition, is that which makes man do his activity well. It is important to emphasize that virtue does not merely make man able to act, but it makes man act in perfect ways. Because there are two parts that have reason, one as obeying reason, the other as itself having reason and thinking, human virtue makes man reason well and listen well to reason.
In addition, one called virtuous always conducts himself in right activities. The right activities are in accord with right reason. However, Aristotle asserts that actions alone are insufficient to manifest virtue, but “we must take someone’s pleasure or pain following on his actions to be a sign of his state.” Obviously, a virtuous person will do right actions, but right actions can be done not only by a virtuous person but also by an vicious person. Thus, right actions must be done by an agent in his right state. In a word, virtue concerns both actions and passions. Furthermore, Aristotle reasons that moral virtue is the mean between two extremes: excess and deficiency. The mean is “correct and wins praise” while the extremes are vices. The mean is determined by reason; that is, by prudent people. For instance, courage is the mean between cowardliness and recklessness. Regarding fear, cowardliness is the excess while recklessness is the deficiency. Regarding daring, they switch positions; that is, cowardliness is the deficiency while recklessness is the excess. In addition, Aristotle emphasizes that the mean must be accounted to a particular individual and a particular circumstance. That is, the mean is not one and the same applied to every case. For instance, the intermediate amount of food one ought to take every day must be different for different people. An athlete needs to consume more than a singer because the athlete consumes energy more than the singer.
 Aristotle, Nicomachean Ethics 1094a.
 Aristotle, Nicomachean Ethics 1094a.
 Aristotle, Nicomachean Ethics 1097b.
 Aristotle, Nicomachean Ethics 1099a.
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 Aristotle, Nicomachean Ethics 1099b.
 Aristotle, Nicomachean Ethics 1100b.
 Aristotle, Nicomachean Ethics 1098a.
 Aristotle, Nicomachean Ethics 1104b.
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 Aristotle, Nicomachean Ethics 1106b.