For Plato, justice is a virtue establishing rational order, with each part performing its appropriate role and not interfering with the proper functioning of other parts. Aristotle says justice consists in what is lawful and fair, with fairness involving equitable distributions and the correction of what is inequitable. For Kant, it is a virtue whereby we respect others’ freedom, autonomy, and dignity by not interfering with their voluntary actions, so long as those do not violate others’ rights.
Plato’s Republic carefully analyses justice. His definition in the first book (331e, 332-b-c) translates to everybody getting what they deserve. Socrates demolishes the view that justice is telling the truth and repaying one’s debts with a counter-example: if a friend lends you weapons, when he is sane, but then wants them back to do great harm, because he has become insane, you should not return them at that time and should even lie to him, if necessary to prevent great harm. Secondly, Socrates destroys the theory that justice is about giving people what is due, depending on whether people are our friends, deserving good from us, or enemies, deserving harm. in stages: first, we are flawed in regarding who are true friends, as opposed to true enemies, so that makes it difficult to say how we should treat people; second, it is as significant whether people are good or bad as whether they are our friends or our enemies; and third, it is not at all clear that justice should excuse or require deliberately harming anyone (Republic, pp. 5-11; 331b-335e).
The third account asserts that justice is relative to whatever is advantageous to the stronger people (politically powerful people in leadership positions). But even the strongest leaders are sometimes mistaken about what is to their own advantage, raising the question of whether people ought to do what leaders suppose is to their own advantage or what actually is so. Socrates suggests three criteria for judgment: which is the smarter, the more secure, and the happier way of life; he argues that the just life is better on all three counts. (ibid., pp. 14-21, 25-31; 338c-345b, 349c-354c).
In the second book of Plato’s Republic, Glaucon says that Socrates has failed to establish any intrinsic value in justice, and challenges him in three steps: first, he argues that justice is a conventional compromise, agreed to by people for their selfish good and socially enforced; second, he illustrates our natural selfish preference for being unjust if we can get away with it by the story of the ring of Gyges, which provides its wearer with invisibility at will and gets away with the most wicked of injustices; and, third, he tries to show that it is better to live unjustly than justly, claiming that it would be better to be the unjust person whom everyone thinks just than the just person who is thought to be unjust. Adeimantus adds that, parents instruct their children to behave justly not because it is good in itself but merely because it tends to pay off for them. (Republic, pp. 33-42; 357b-366e). Therefore, the challenge for Socrates is to show the true nature of justice and that it is intrinsically valuable rather than only desirable for its contingent consequences.
Plato has Socrates construct his own positive theory, that justice is essential of both a good political state and a good personal character. In Book IV, Socrates and Glaucon agree that, if they succeed in establishing the foundations of a “completely good” society, it would comprise of four virtues: wisdom, courage, temperance, and justice. If they can identify the first three, whatever remains essential to a completely good society is justice. It then turns out that “justice is doing one’s own work and not meddling with what isn’t one’s own”: the positive side is each person doing their assigned tasks; the negative not interfering with others doing their appointed tasks. Socrates presents an analogy suggesting that a “completely good” soul would also have the same four virtues. A good soul is wise, in having good judgment whereby reason rules; courageous in that its spirited part is willing to fight for its convictions in the face of fear; and temperate, because all parts agree that it should be always under the command of reason. There are also four vices, foolishness, cowardice, self-indulgence, and injustice. Therefore, we show that justice is better than injustice in itself and not merely for its likely consequences, because justice is the health of the soul. Just as health is intrinsically and not just instrumentally good, so is justice; injustice is a disease—to be avoided even without any undesirable consequences, even if nobody is aware of it. (ibid., pp. 43, 102-121; 368d, 427d-445b)
Plato applies this theory of justice to a social issue in Book V, arguing for equal opportunity for women. Plato says that, even though women tend to be physically weaker than men, this should prevent them from being educated for the same socio-political functions as men, including top ranks of leadership responsibility. While the body has a gender, it is the soul that is virtuous or vicious. Despite their different roles in procreation, there is no reason why a woman should not be as intelligent and virtuous as men, if properly taught. As much as possible, men and women should share the workload in common. (Republic, pp. 125-131; 451d-457d).
In Politics, Aristotle political justice’s relation to equality. He agrees with Plato that political democracy is intrinsically unjust because it treats unequals as equals. Justice rather requires inequality for people who are unequal. But treating equals as unequal because of birth, wealth, etc is unjust. Rather, those in a just political society who contribute the most to the common good will receive a larger share, because they show more political virtue. Political justice is viewed as a function of the common good of a community. Aristotle thinks that political justice requires “proportional” rather than numerical equality. But inferiors have a vested interest those who are equal in some respect being equal in all respects, while superiors are biased towards those who are unequal in some way being unequal in all ways. For example, those who are equally citizens are not necessarily equal in political virtue, and those who are financially richer are not necessarily morally or mentally superior. He suggests that “equality according to merit,” must involve moral and intellectual virtue. (Politics, pp. 79, 81, 86, 134, 136, 151, 153; 1280a, 1281a, 1282b, 1301a-1302a, 1307a, 1308a)
While Plato accepted slavery as a legitimate social institution but argued for equal opportunity for women, in Politics, Aristotle accepts sexual inequality while actively defending slavery. A human being can be naturally autonomous or not, “a natural slave”; and can be regarded as “a piece of property,” or another person’s “tool for action.” Aristotle says that some are marked as superior and fit to rule from birth, while others are inferior and marked from birth to be ruled by others. This applies not only to ethnic groups, but also to genders, and he asserts that males are “naturally superior” and females “naturally inferior,” the former being fit to rule and the latter to be ruled. He claims it is naturally better for women to be ruled by men, as it is better for “natural slaves” to be ruled by the “naturally free.” Aristotle argues for natural slavery. It was the custom to make slaves of conquered enemies who become prisoners of war, but like Plato, he believes that Greeks are born for free and rational self-rule, unlike non-Greeks (“barbarians”), who are naturally inferior and incapable of it. Aristotle justifies the alleged inequality among them based on what he calls the “deliberative” capacity of their rational souls. The n
atural slave’s rational soul supposedly lacks this, a woman has it, but it lacks the authority to be autonomous, a (free male) child has it in some developmental stage, and a naturally superior free male has it developed and available for governance. (ibid., pp. 7-11, 23; 1254a-1255a, 1260a).
Like Plato, Aristotle argues for an objective theory of personal and social justice as a preferable alternative to the relativistic one of the Sophists. Aristotle’s empirical (as opposed to Plato’s idealistic) approach to justice put him in the position of needing to claim how things ought to be rather than the way things actually are. It also leaves Aristotle with little means of establishing a universal perspective that respects the equal dignity of all humans. Therefore, his theory, like Plato’s, fails to respect all people as free, rational beings. They were so focused on the ways in which people are unequal, that they could not appreciate a fundamental moral equality that might provide a platform for natural human rights.
Kant insists that humans should not live on earth unless justice prevails (Metaphysics of Moral, 6:332). He describes “right” by stating three conditions for something to be enforceable (6:230). First, right concerns only actions that have influence on other people, directly or indirectly. Second, right does not concern desires but choices that generate actions. Third, right does not concern the matter of the other’s act but only the form. As an example, Kant mentions trade. To be rightful, trade must be freely agreed on by both parties but can have any matter or purpose the traders want. The central thought in the Doctrine of Right is the Principle of Right: Any action is right if it can coexist with everyone’s freedom in accordance with a universal law (6:230). The Principle of Right can be considered as the application of the Categorical Imperative to the political context where strangers live together under one jurisdiction and where coercive state power implements public choices.
The condition of distributive justice, Kant explains, is the rightful condition under which a state realises the Principle of Right (6:307). What the state “distributes” is access to institutions that make sure everybody gets what is theirs. Distributive justice is public law securing private right. Kant defines a judge’s verdict as “an individual act of public justice” (6:317). The right sort of public administration cannot involve any deception and illegitimate force (force not needed to remove a hindrance to freedom, 6:231).
Kant believed that without freedom, there is not justice. The state is justified to coerce only to remove a hindrance to freedom. Freedom involves the right of individuals to conceive of happiness their own way, but a state cannot legitimately impose a conception of happiness on its citizens. Kant advocates the duty of supporting fellow-citizens who cannot support themselves and gives the state the power to provide this help. The point is that individuals cannot live together in a state unless they make the state responsible for the support of the poor. Moreover, the state is charged with self-maintenance, therefore has the power to “administer the state’s economy, finances and police”.
The basic features of Kant’s moral philosophy are: it’s rule based (establishing the difference between right and wrong and creating moral rules, as opposed to practical ethics which look at individual moral dilemmas and tries to figure out what the ethically correct response might be), values autonomy (everyone should arrive at his conclusions by exercising their own reason, rather than taking his word for it), holds that people can never be used as means to an end (i.e. you can’t kill or manipulate people “for the greater good”), and holds that rationality is key to making the right decisions in ethical situations. It is often praised for providing people with a relatively simple decision-making procedure to use when making an ethical decision and criticised for its rigidity and lack of emotion.
By contrast, Plato’s ethics are virtue-based and not as concerned with how we should act as with how we should live, and more with well-being than moral. Plato and Aristotle were more concerned with how people should live their lives to be happy than with the difference between right and wrong. They wanted to achieve the optimal state of being for any human, and help their fellows achieve it as well. They all shared a belief that being a good person was essential for accomplishing this and believed that it could be achieved through cultivating various virtues and eliminating vices.
While Kant thought that to make the best decisions in life, one should think them through rationally, Plato believed that as we rely on our instincts, they should be our focus – by training to be a good person, one would act the right way without having to think about it. That said, Plato supported rationality. One could adopt a Platonic virtue ethic and decide that it is virtuous to know the difference between right and wrong, and then use Kant’s categorical imperative to help them with this. However, Plato was not in favour of autonomy; his ideal state, said in the Republic, was one in which the ruling class decided what people should do.
To conclude we can ask, why should we be just? For Plato, this is the way to achieve the fulfilment of a well-ordered soul. For Aristotle, the achievement and exercising of moral virtue is a necessary condition of human flourishing. For Kant, we should try to be just because it’s the right thing to do and because it is our duty, as rational, moral agents, to try to do what is right.