In reality, services are scarcely ever exchanged directly. There is a medium, which is termed _money_. Paul has completed a coat, for which he wishes to receive a little bread, a little wine, a little oil, a visit from a doctor, a ticket for the play, etc. The exchange cannot be effected in kind; so what does Paul do? He first exchanges his coat for some money, which is called _sale_; then he exchanges this money again for the things which he wants, which is called _purchase_; and now, only, has the reciprocity of services completed its circuit; now, only, the labor and the compensation are balanced in the same individual,--"I have done this for society, it has done that for me." In a word, it is only now that the exchange is actually accomplished. Thus, nothing can be more correct than this observation of J.B. Say: "Since the introduction of money, every exchange is resolved into two elements, _sale_ and _purchase_. It is the reunion of these two elements which renders the exchange complete." We must remark, also, that the constant appearance of money in every exchange has overturned and misled all our ideas; men have ended in thinking that money was true riches, and that to multiply it was to multiply services and products. Hence the prohibitory system; hence paper money; hence the celebrated aphorism, "What one gains the other loses;" and all the errors which have ruined the earth, and imbrued it with blood.[17] After much research it has been found, that in order to make the two services exchanged of equivalent value, and in order to render the exchange _equitable_, the best means was to allow it to be free. However plausible, at first sight, the intervention of the State might be, it was soon perceived that it is always oppressive to one or other of the contracting parties. When we look into these subjects, we are always compelled to reason upon this maxim, that _equal value_ results from liberty. We have, in fact, no other means of knowing whether, at a given moment, two services are of the same value, but that of examining whether they can be readily and freely exchanged. Allow the State, which is the same thing as force, to interfere on one side or the other, and from that moment all the means of appreciation will be complicated and entangled, instead of becoming clear. It ought to be the part of the State to prevent, and, above all, to repress artifice and fraud; that is, to secure liberty, and not to violate it. I have enlarged a little upon exchange, although loan is my principal object: my excuse is, that I conceive that there is in a loan an actual exchange, an actual service rendered by the lender, and which makes the borrower liable to an equivalent service,--two services, whose comparative value can only be appreciated, like that of all possible services, by freedom. Now, if it is so, the perfect lawfulness of what is called house-rent, farm-rent, interest, will be explained and justified. Let us consider the case of _loan_.