Socrates proceeds to discover the nature of justice by a method of residues. Each of the first three virtues corresponds to one of the three parts of the soul and one of the three classes in the State, although the third, temperance, has more of the nature of a harmony than the first two. If there be a fourth virtue, that can only be sought for in the relation of the three parts in the soul or classes in the State to one another. It is obvious and simple, and for that very reason has not been found out. The modern logician will be inclined to object that ideas cannot be separated like chemical substances, but that they run into one another and may be only different aspects or names of the same thing, and such in this instance appears to be the case. For the definition here given of justice is verbally the same as one of the definitions of temperance given by Socrates in the Charmides (162 A), which however is only provisional, and is afterwards rejected. And so far from justice remaining over when the other virtues are eliminated, the justice and temperance of the Republic can with difficulty be distinguished. Temperance appears to be the virtue of a part only, and one of three, whereas justice is a universal virtue of the whole soul. Yet on the other hand temperance is also described as a sort of harmony, and in this respect is akin to justice. Justice seems to differ from temperance in degree rather than in kind; whereas temperance is the harmony of discordant elements, justice is the perfect order by which all natures and classes do their own business, the right man in the right place, the division and co-operation of all the citizens. Justice, again, is a more abstract notion than the other virtues, and therefore, from Plato's point of view, the foundation of them, to which they are referred and which in idea precedes them. The proposal to omit temperance is a mere trick of style intended to avoid monotony (cp. vii. 528). There is a famous question discussed in one of the earlier Dialogues of Plato (Protagoras, 329, 330; cp. Arist. Nic. Ethics, vi. 13. 6), 'Whether the virtues are one or many?' This receives an answer which is to the effect that there are four cardinal virtues {lxiv} (now for the first time brought together in ethical philosophy), and one supreme over the rest, which is not like Aristotle's conception of universal justice, virtue relative to others, but the whole of virtue relative to the parts. To this universal conception of justice or order in the first education and in the moral nature of man, the still more universal conception of the good in the second education and in the sphere of speculative knowledge seems to succeed. Both might be equally described by the terms 'law,' 'order,' 'harmony;' but while the idea of good embraces 'all time and all existence,' the conception of justice is not extended beyond man. [Sidenote: _Republic IV._ Analysis.]