Justice
The virtue of justice is one of the peaks of virtue, since being truly just requires having all the other virtues as well. In this sense, justice unifies and orders the virtues.
Aristotle also makes a distinction between natural justice and legal justice. Natural justice is the same in all times and places. It is, in a sense, comprised by the laws that order the universe and that order beings toward their ends. Aristotle does admit that from observation it may difficult to see the existence of this natural justice. The reason is that governments vary and no perfect regime exists; thus there seem to be different definitions of justice implied by the laws of each regime. Legal justice is that which is just according to law; it ought to be in accordance with natural justice.
In theory, then, there exists a universal standard of natural justice which is unchangeable, but in practice there must always be a mix of natural justice and legal justice in the laws of the city. Therefore while the principles of natural justice don't change, natural justice in action varies because in applying natural justice conventional justice needs to be added.
Law
All laws are in some sense just, since any law is better than no law. Yet to be truly just a law must be in accordance with natural justice. A problem with laws is that they need to formulated in a universal way and thus are not able to take into account the particulars of each situation. Judges should make up for this shortcoming in the law by basing their decisions not necessarily on what the law actually says but on the reasoning behind the law.
Law is also crucial for the moral education of citizens. Since "passion seems to yield not to argument but to force," laws are necessary in order to habituate citizens in virtuous action. Laws are thus especially necessary for the young, so that at an early age their passions will be properly trained and they will learn to take pleasure in what is virtuous. Yet since in any city there will be a great number of adults who are not virtuous, laws are necessary for one's entire life.
The Good
Aristotle begins Nicomachean Ethics by asserting that there is some ultimate good which is both final and self-sufficient, and he defines this good as happiness. There must be one final end of all human actions, because a human action by definition is one which is done on purpose and for a definite goal. An action may be performed for a limited goal, but that goal is a means to larger goal which is a means to another even larger goal, and so on, until one reaches the final goal which is desired for its own sake. All lesser goods, such as wealth, honor, fame, glory, pleasure, et cetera are not desired for themselves but in order to attain happiness. That this supreme good is happiness has never really been a cause of dispute, for according to Aristotle, "we may almost say that the great majority of mankind are agreed about this; for both the multitude and persons of refinement speak of it as Happiness, and conceive the good life' or doing well' to be the same thing as being happy."
Happiness
Aristotle holds that the happiness of man can be defined by determining the function proper to man. This function cannot be one which plants and animals also perform, because it must be particular to human beings. Therefore, man's function must be a part of the practical life of the rational part of man, the term practical implying purposeful conduct, which is possible only for rational beings. It follows, then, that happiness consists in the action of the rational part of man, the soul. The ultimate good of man should naturally flow from performing his function well; therefore, as Aristotle theorizes, "the Good of man [and, by extension, the definition of happiness] is the active exercise of his soul's faculties in conformity with excellence or virtue, or if there be several human excellences or virtues, in conformity with the best and most perfect among them." To constitute true happiness this action must persist with continuity throughout a lifetime. The highest happiness for a human being is a life of contemplation, but secondary happiness is achieved through ethical virtue.
Virtue
In Nicomachean Ethics Aristotle discusses eleven virtues: courage, temperance, generosity, magnificence, magnanimity, right ambition, good temper, friendliness, truthfulness, wit, and justice. Virtue is a mean by two extremes, and its exercise thus requires prudence in order to determine what the mean is for specific circumstances. Virtues are acquired by habituation. Acting virtuously is not the same as being virtuous, but acting virtuously is the means to become virtuous. The four requirements for virtue are that the person (1) know what he is doing, (2) intend the action for its own sake, (3) take pleasure in it and (4) do it with certainty and firmness. When a person performs a virtuous action but does it in opposition to his desires, he is continent but not virtuous.
Human Nature
All human beings naturally desire the good, which is happiness. The highest faculty of a human being is the ability to reason. Through reason humans, unlike animals, can examine things beyond the material and sensible level and can reach conclusions about the nature of things. Human beings have the ability to choose their actions freely, an ability which is a prerequisite for morality. The end or goal of human life can be discovered through a rational analysis of human nature by examining the highest faculties of a human being. The best life for a human being is one which is in accord with a person's highest ability, which is reason. Human beings are also social by nature, as shown by the natural desire for friendship and by the ability of human beings to speak and communicate with others.
Wealth
While some live as if wealth were the ultimate aim of human life, they are incorrect in doing so, for wealth is only an instrumental good and is not an end in itself. Some external goods are necessary for happiness, though for the highest happinessthat is, the contemplative lifea moderate amount of wealth sufficient to provide a person's physical needs is better than superfluous wealth. Generosity and munificence are both virtues which direct the use of wealth. A person should use his wealth liberally in the service of others and of good causes, but should not spend beyond his means.
Prudence
The virtue which one must develop in order to attain moral virtue and to find the correct mean in all of one's actions is prudence. Prudence is an intellectual virtue, and is the ability to deliberate well regarding human actions. Concerned with particulars of action, prudence is absolutely necessary in order to find the mean, or in Aristotle's words, "to know what is good for oneself" (1142a). The philosopher even goes so far as to say that "without prudence virtues cannot exist," but that where there is prudence, "all the others are present" (1144b). Prudence and ethical virtue are in fact inseparable, much like two sides of the same coin, "for while virtue makes the end in view right, prudence makes the means towards it right" (1144a).
Friendship
Friendship is necessary for a happy life, because human beings are social beings. There are three types of friendshipthose based on useful, those based on pleasure, and those based on virtue. Only the third type of friendship is friendship in the complete sense. Friendship requires that the friends wish the good for one another and share in some of life's activities together. A friend is another self, and the love one has for a friend is analogous to proper self-love. Friends help one another to grow in self-knowledge and in virtue. The disposition proper to a friend is to love.
