What implications does this have for Plato’s discussion of justice in the Republic? Socrates, Plato’s narrator, opens in book one by attacking Thrasymachus who is representative of the ‘Athenian’ viewpoint. Thrasymachus maintains that justice is, and should be, guided by self - interest; justice is what is in the interest of the stronger. Morality, for example, exists by common agreement to reinforce the dominance of the stronger over the weaker. Socrates however exposes a contradiction in this argument: subjects, Thrasymachus maintains, must act according to the rules they make (the most basic principle of the rule of law). Rulers (rulers who are not philosophers, it is understood) are fallible and make mistakes; they occasionally act in a way which is actually not in their interest. It is right and just that subjects still obey their leaders even when they may be wrong, therefore acting in the interest of a weaker party. "Then according to your argument it is right not only to do what is in the interest of the stronger party but also the opposite." In opposition here is the conception of justice as truly individual self - interest, whereby everyone is fighting everyone else, and self - interested ‘justice’ on a social scale, where the stronger are supposed to eschew self - interest for a common goal. As Socrates quickly makes clear, this argument will not suffice as a useful concept of justice. What it needs in definition is philosophy - the considered approach.
Plato, through his narrator Socrates, slowly begins to build up his definition of justice. The body has, at its most basic level, needs. It is not self - sufficient, at least beyond that of mere subsistence. "[the body] certainly has needs. That is the reason why medicine has been discovered, because the body has defects and is not self - sufficient; medical skill was, in fact, developed to look after the interests of the body." Doctors, to use one of Socrates’ many examples, "prescribes with a view not to his own interest but that of his patient." Each person’s particular skill has its function within society, and using the body as an analogy, Socrates illustrates how everyone, keeping to and developing their own particular excellence, benefits themselves while also contributing to a more just and therefore better whole.
"...we can say that the ears, if deprived of their own peculiar excellence, perform their function badly...Is there any function that is impossible to perform with anything except the mind? For example, paying attention, controlling, deliberating, and so on...It follows that a good mind will perform the functions of control and attention well, and a bad mind badly...And we agreed, did we not, that justice was the peculiar excellence of the mind and injustice its defect?...So the just mind and the just man will have a good life, and the unjust a bad life?"
Socrates has attempted to show how the just man will lead a happier life, that justice is more than something which corresponds only to the ideas and actions of the stronger party in some social interaction, and thus variable and subjective, but has a universal meaning through which the individual (in Plato’s metaphor) or society (as he is implicitly referring to) will concretely benefit. ‘Justice,’ then is each person pursuing their own excellences and not interfering with that of others, to the benefit of everyone.
Plato’s use of the body as a metaphor for society is significant. Radically dissimilar to the mainstream of ‘modern’ political thought, Plato attempted not to draw much distinction between the individual body and the wider political community. Plato’s assertion that all humans are by their very nature political was an expression of this fundamental, peculiarly ‘ancient’ idea. By this token, as knowledge or philosophy in a basic sense, is applied on an individual level, to carry out everyday tasks, it too should be applied in the wider sense.
Plato later in the Republic, identifies three elements of the human soul, or psyche. Different elements will come to prominence under differing political arrangements. There exists, says Plato, desire or appetite on one extreme and reason or rationality on the other. Inbetween is thymos, a vague category often translated as ‘spirit’ or ‘will’. A concept of justice expressed by Thrasymachus as that which is in the interest of the stronger party owes its origin to the dominance of desire. Reason however Plato considers the superior element of the soul. An understanding of justice then requires not instinctual ‘political’ (in the most basic sense) judgements, changeable and merely contextual relevant, but a rational and reasoned philosophical base. Justice requires knowledge. "Isn’t it characteristic of the honourable to subjugate the bestial parts of human nature to the human part (we might, perhaps, rather call it the divine part) ?" Plato asks for philosophy to bring humanity towards another ideal which cynical modern political theory has long abandoned, that of the summun bonnum, the ‘highest good, realised in the perfect state. Plato acknowledges human imperfection, "...sometimes a person’s nature has some sort of weakness in its best aspect, which makes that aspect able only to minister to the broods of desires within him, and not to rule them," but it is then the purpose of philosopher - rulers to educate and rule in a way which "impress[es] upon him [the man ruled by desire] from outside, so that as far as possible we may all be alike and all be friends, since we are all steered by the same helmsman." The ‘ship of state’ (the metaphor to which Plato here is referring) must be sailed by philosophers, those possessed with knowledge of the forms and not seduced through desire by mere appearances, which is for the benefit of all.
Philosophy plays a large part in the discussion of justice in the Republic because this, the pursuit of philosophy, is the basis of the platonic project. This application of idealism to practical situations has dominated political thinking from Plato until the late nineteenth century; modern political philosophy has been summarised succinctly as ‘footnotes to Plato.’ Plato’s ideas had practical ends - he established his Academy to train philosopher rulers and realise the proposals in the Republic, but it was theory which determined practice and without solid theory, practical failure (such as the defeat of his native Athens at the hands of Sparta) would surely follow.