And further, money is a kind of security to us in respect of exchange at some future time (supposing that one wants nothing now that we shall have it when we do): the theory of money being that whenever one brings it one can receive commodities in exchange: of course this too is liable to depreciation, for its purchasing power is not always the same, but still it is of a more permanent nature than the commodities it represents. And this is the reason why all things should have a price set upon them, because thus there may be exchange at any time, and if exchange then dealing. So money, like a measure, making all things commensurable equalises them: for if there was not exchange there would not have been dealing, nor exchange if there were not equality, nor equality if there were not the capacity of being commensurate: it is impossible that things so greatly different should be really commensurate, but we can approximate sufficiently for all practical purposes in reference to Demand. The common measure must be some one thing, and also from agreement (for which reason it is called νόμισμα), for this makes all things commensurable: in fact, all things are measured by money. Let B represent ten minæ, A a house worth five minæ, or in other words half B, C a bed worth 1/10th of B: it is clear then how many beds are equal to one house, namely, five. It is obvious also that exchange was thus conducted before the existence of money: for it makes no difference whether you give for a house five beds or the price of five beds. Chapter IX. We have now said then what the abstract Just and Unjust are, and these having been defined it is plain that just acting is a mean between acting unjustly and being acted unjustly towards: the former being equivalent to having more, and the latter to having less. But Justice, it must be observed, is a mean state not after the same manner as the forementioned virtues, but because it aims at producing the mean, while Injustice occupies _both_ the extremes. And Justice is the moral state in virtue of which the just man is said to have the aptitude for practising the Just in the way of moral choice, and for making division between, himself and another, or between two other men, not so as to give to himself the greater and to his neighbour the less share of what is choice-worthy and contrariwise of what is hurtful, but what is proportionably equal, and in like manner when adjudging the rights of two other men.