The view is also held by some that simple Reciprocity is Justice. This was the doctrine of the Pythagoreans, who defined the just simply as “suffering reciprocally with another.”¹ Reciprocity however does not coincide either with Distributive or with Corrective Justice (although people mean to identify it with the latter when they quote the rule of Rhadamanthys— An a man suffer even that which he did, Right justice will be done). For in many cases Reciprocity is at variance with Justice: for example, if an officer strikes a man, it is wrong for the man to strike him back; and if a man strikes an officer, it is not enough for the officer to strike him, but he ought to be punished as well. Again, it makes a great difference whether an act was done with or without the consent of the other party.² But in the interchange of services Justice in the form of Reciprocity is the bond that maintains the association: reciprocity, that is, on the basis of proportion, not on the basis of equality. The very existence of the state depends on proportionate reciprocity; for men demand that they shall be able to requite evil with evil—1133aif they cannot, they feel they are in the position of slaves—and to repay good with good— failing which, no exchange takes place, and it is exchange that binds them together. This is why we set up a shrine of the Graces in a public place, to remind men to return a kindness; for that is a special characteristic of grace, since it is a duty not only to repay a service done one, but another time to take the initiative in doing a service oneself. Now proportionate requital is effected by diagonal conjunction. For example, let A be a builder, B a shoemaker, C a house, and D a shoe. It is required that the builder shall receive from the shoemaker a portion of the product of his labor, and give him a portion of the product of his own. Now³ if proportionate equality between the products be first established, and then reciprocation take place, the requirement indicated will have been achieved; but if this is not done, the bargain is not equal, and intercourse does not continue. For it may happen that the product of one of the parties is worth more than that of the other, and in that case therefore they have to be equalized. This holds good with the other arts as well; for they would have passed out of existence if the active element did not produce, and did not receive the equivalent in quantity and quality of what the passive element receives.⁴ For an association for interchange of services is not formed between two physicians, but between a physician and a farmer, and generally between persons who are different, and who may be unequal, though in that case they have to be equalized. Hence all commodities exchanged must be able to be compared in some way. It is to meet this requirement that men have introduced money; money constitutes in a manner a middle term, for it is a measure of all things, and so of their superior or inferior value, that is to say, how many shoes are equivalent to a house or to a given quantity of food. As therefore a builder is to a shoemaker,⁵ so must such and such a number of shoes be to a house, [or to a given quantity of food]⁶; for without this reciprocal proportion, there can be no exchange and no association; and it cannot be secured unless the commodities in question be equal in a sense. It is therefore necessary that all commodities shall be measured by some one standard, as was said before. And this standard is in reality demand, which is what holds everything together, since if men cease to have wants or if their wants alter, exchange will go on no longer, or will be on different lines. But demand has come to be conventionally represented by money; this is why money is called nomisma (customary currency), because it does not exist by nature but by custom (nomos), and can be altered and rendered useless⁷ at will. There will therefore be reciprocal proportion when the products have been equated, so that as farmer is to shoemaker,⁸ so may the shoemaker’s product be to the farmer’s product. 1133bAnd when they exchange their products they must reduce them to the form of a proportion, otherwise one of the two extremes will have both the excesses⁹; whereas when they have their own,¹⁰ they then are equal, and can form an association together, because equality in this sense can be established in their case (farmer A, food C, shoemaker B, shoemaker’s product equalized D¹¹); whereas if it were impossible for reciprocal proportion to be effected in this way, there could be no association between them. That it is demand which, by serving as a single standard, holds such an association together, is shown by the fact that, when there is no demand for mutual service on the part of both or at least of one of the parties, no exchange takes place between them [as when someone needs something that one has oneself, for instance the state offering a license to export corn in exchange for wine].¹² This inequality of demand has therefore to be equalized. Now money serves us as a guarantee of exchange in the future: supposing we need nothing at the moment, it ensures that exchange shall be possible when a need arises, for it meets the requirement of something we can produce in payment so as to obtain the thing we need. Money, it is true, is liable to the same fluctuation of demand as other commodities, for its purchasing power varies at different times; but it tends to be comparatively constant. Hence the proper thing is for all commodities to have their prices fixed; this will ensure that exchange, and consequently association, shall always be possible. Money then serves as a measure which makes things commensurable and so reduces them to equality. If there were no exchange there would be no association, and there can be no exchange without equality, and no equality without commensurability. Though therefore it is impossible for things so different to become commensurable in the strict sense, our demand furnishes a sufficiently accurate common measure for practical purposes. There must therefore be some one standard, and this accepted by agreement (which is why it is called nomisma, customary currency); for such a standard makes all things commensurable, since all things can be measured by money. Let A be a house, B ten minae and C a bedstead. Then A=B/2 (supposing the house to be worth, or equal to, five minae), and C (the bedstead) =B/10; it is now clear how many bedsteads are equal to one house, namely five. It is clear that before money existed this is how the rate of exchange was actually stated—five beds for a house—since there is no real difference between that and the price of five beds for a house. We have now stated what Justice and Injustice are in principle. From the definition given, it is plain that just conduct is a mean between doing and suffering injustice, for the former is to have too much and the latter to have too little. And Justice is a mode of observing the mean, though not in the same way as the other virtues are, but because it is related to a mean, while Injustice is related to the extremes. 1134aAlso, Justice is that quality in virtue of which a man is said to be disposed to do by deliberate choice that which is just, and, when distributing things between himself and another, or between two others, not to give too much to himself and too little to his neighbor of what is desirable, and too little to himself and too much to his neighbor of what is harmful, but to each what is proportionately equal; and similarly when he is distributing between two other persons. Injustice on the contrary is similarly related to that which is unjust, which is a disproportionate excess or deficiency of something beneficial or harmful. Hence Injustice is excess and defect, in the sense that it results in excess and defect: namely, in the offender’s own case, an excess of anything that is generally speaking beneficial and a deficiency of anything harmful, and in the case of others,¹³ though the result as a whole is the same, the deviation from proportion may be in either direction as the case may be. Of the injustice done, the smaller part is the suffering and the larger part the doing of injustice. So much may be said about the nature of Justice and Injustice, and of the Just and the Unjust regarded universally.¹⁴

But seeing that a man may commit injustice without actually being unjust, what is it that distinguishes those unjust acts the commission of which renders a man actually unjust under one of the various forms of injustice, for example, a thief or an adulterer or a brigand? Or shall we rather say that the distinction does not lie in the quality of the act? For a man may have intercourse with a woman knowing who she is, yet not from the motive of deliberate choice, but under the influence of passion; in such a case, though he has committed injustice, he is not an unjust man: for instance, he is not a thief, though guilty of theft, not an adulterer, though he has committed adultery, and so forth. The relation of Reciprocity to Justice has been stated already. But we must not forget that the subject of our investigation is at once Justice in the absolute sense and Political Justice. Political Justice means justice as between free and (actually or proportionately) equal persons, living a common life for the purpose of satisfying their needs. Hence between people not free and equal political justice cannot exist, but only a sort of justice in a metaphorical sense. For justice can only exist between those whose mutual relations are regulated by law, and law exists among those between whom there is a possibility of injustice, for the administration of the law means the discrimination of what is just and what is unjust. Persons therefore between whom injustice can exist can act unjustly towards each other (although unjust action does not necessarily involve injustice): to act unjustly meaning to assign oneself too large a share of things generally good and too small a share of things generally evil. This is why we do not permit a man to rule, but the law, because a man rules in his own interest, 1134band becomes a tyrant; but the function of a ruler is to be the guardian of justice, and if of justice, then of equality. A just ruler seems to make nothing out of his office; for he does not allot to himself a larger share of things generally good, unless it be proportionate to his merits; so that he labors for others, which accounts for the saying mentioned above,¹⁵ that “Justice is the good of others.” Consequently some recompense has to be given him, in the shape of honor and dignity. It is those whom such rewards do not satisfy who make themselves tyrants. Justice between master and slave and between father and child is not the same as absolute and political justice, but only analogous to them. For there is no such thing as injustice in the absolute sense towards what is one’s own; and a chattel,¹⁶ or a child till it reaches a certain age and becomes independent, is, as it were, a part of oneself, and no one chooses to harm himself; hence there can be no injustice towards them, and therefore nothing just or unjust in the political sense. For these, as we saw, are embodied in law, and exist between persons whose relations are naturally regulated by law, that is, persons who share equally in ruling and being ruled. Hence Justice exists in a fuller degree between husband and wife than between father and children, or master and slaves; in fact, justice between husband and wife is Domestic Justice in the real sense, though this too is different from Political Justice.