Plato's interpretation of justice as seen in 'The Republic' is a vastly different one when compared to what we and even the philosophers of his own time are accustomed to. Plato would say justice is the act of carrying out one's duties as he is fitted with. Moreover, if one's duties require one to lie or commit something else that is not traditionally viewed along with justice; that too is considered just by Plato's accounts in 'The Republic.' I believe Plato's account of justice, and his likely defense against objections are both clear and logical, thus I will endeavor to argue his views as best as I can. Plato's view of justice ties in with his view of a perfect world. In Plato's ideal world, the society would be a wise one, wise in understanding that their own position in society is just.
This society in turn, must carry out their duties fitted to them by their position. Unfortunately the real world does not function in that manner, Plato understanding that 'fault' with society tells us that if the society is lacking wisdom, the most wise ones would be philosophers, (473 d) and society should consider them to be the authority. Plato believes that being just is so innately important that everyone is better off being just than unjust, no matter the situation. Plato in 360 e-362 d uses Glaucon to make this point, Glaucon asks who is better off? The just or the unjust, given the premises that the unjust man is rich, famous, respected, and powerful and that the just man is poor, defamed, and lives a life of suffering. Plato's only real way to answer this is to prove that justice is innately good and that injustice is innately evil; simply prove the poor, defamed man happy and the rich, respected unjust man unhappy. Plato goes about this by explaining what justice is; justice has to do with doing what is right, and there exists some specific virtue in everything, which enables it to work well.
If it is deprived of that nature, in contrast it would suffer. It is much the same with the soul, the soul must also perform its specific virtue. The more virtuous, or 'just' a soul is, the happier the soul is. The happier the soul is, the happier the person is.
Therefore a just man lives happily and well, whereas an unjust man would not. This argument follows the a = b b = c therefore a = c argument form. Another objection, brought about by a radical and different theory of Justice is brought up by Plato in a conversation between Socrates and Thrasymachus. In this argument Thrasymachus defines justice as in the interest of the stronger. This basically means that justice belongs in the hands of the rulers, and that the rulers are whoever is stronger, therefore getting to a ruling position. Laws are then made, based on the ruling party's interest, and only theirs.
Those who violate such created laws, will get punished for breaking the law and so on and so forth. Socrates completely disagrees with this theory of justice and gives the analogy of a physician who is studying and exercising his power is in fact doing so in the interest of his patients, not himself. In the same manner, the government will do what is in the interest of the people, and not of itself. Some unanswered objections that may come up against Plato's idea of justice may target the part where he believes that philosophers are the only qualified individuals to run his ideal society. Plato believes that philosophers have knowledge, I pose a scenario where there are no more philosophers, perhaps because of a philosopher massacre, or one where there is simply nobody wise enough. One can easily make the argument that since philosophy is dealing with the same questions for the past 2500 years, that we are actually not wise, and in fact quite the opposite.
I believe that for the most part, Plato has a successful account of justice. Plato's criticism of then present theories of justice and his defense against the xxx xxx theories make sense logically. Furthermore, Plato was ages ahead of his time by arguing for equal rights among men and woman when concerning the guardians, unlike Aristotle who got almost everything wrong and most likely set philosophy and other sciences back centuries, I believe Plato was ages ahead of his time in understand that men and women are equal in at least the 'capacity to understand reality and make reasonable judgments about it.' (454 d) However; just that fact does not lead to a proper defense against arguments. One thing a reader may have a problem is that Plato seems to be showing a little Heidegger by alluding to a dictatorship which are ruled by the wise, namely, philosophers.
Even if such a Nazi and Communist-es que dictatorship were to be implemented, I fear it would hit the same brick wall that other dictatorships face, the people will not sit idly by while they are told what to do. I believe that leads to a larger problem. Plato seemingly wants to hint more and more at an innate knowledge which includes justice, or if the person does not have this innate knowledge he can be taught in society: knowledge and the just thing to do. I believe this poses a problem for Plato, if society innately knows the correct thing to do, but does not do it, then this is contradictory with the definition of justice Plato wants for us.
And if there is one thing philosophers have insisted upon over time is that there are no contradictions. In its defense; I do not know of any philosophical questions that have a complete answer, otherwise there would be no more philosophy. Even with the possible shortcomings, Plato argues his justice logically, and uses Glaucon and Adeimentus well, to show the strengths of his arguments.