notion of value) that the second form is always implied in the first. When it is said, "Do this for me, and I will do that for you," an exchange of service for service is proposed. Again, when it is said, "Give me this, and I will give you that," it is the same as saying, "I yield to you what I have done, yield to me what you have done." The labour is past, instead of present; but the exchange is not the less governed by the comparative valuation of the two services: so that it is quite correct to say that the principle of value is in the services rendered and received on account of the productions exchanged, rather than in the productions themselves.
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, &c. 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 labour 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,
