Suppose two men exchange two services or two objects, whose equal value is beyond all dispute. Suppose, for example, Peter says to Paul, "Give me ten sixpences, I will give you a five-shilling piece." We cannot imagine an equal value more unquestionable. When the bargain is made, neither party has any claim upon the other. The exchanged services are equal. Thus it follows, that if one of the parties wishes to introduce into the bargain an additional clause, advantageous to himself, but unfavourable to the other party, he must agree to a second clause, which shall re-establish the equilibrium, and the law of justice. It would be absurd to deny the justice of a second clause of compensation. This granted, we will suppose that Peter, after having said to Paul, "Give me ten sixpences, I will give you a crown," adds, "You shall give me the ten sixpences _now_, and I will give you the crown-piece _in a year_;" it is very evident that this new proposition alters the claims and advantages of the bargain; that it alters the proportion of the two services. Does it not appear plainly enough, in fact, that Peter asks of Paul a new and an additional service; one of a different kind? Is it not as if he had said, "Render me the service of allowing me to use for my profit, for a year, five shillings which belong to you, and which you might have used for yourself?" And what good reason have you to maintain that Paul is bound to render this especial service gratuitously; that he has no right to demand anything more in consequence of this requisition; that the State ought to interfere to force him to submit? Is it not incomprehensible that the economist, who preaches such a doctrine to the people, can reconcile it with his principle of _the reciprocity of services_? Here I have introduced cash; I have been led to do so by a desire to place, side by side, two objects of exchange, of a perfect and indisputable equality of value. I was anxious to be prepared for objections; but, on the other hand, my demonstration would have been more striking still, if I had illustrated my principle by an agreement for exchanging the services or the productions themselves.