Do these sacrifices invalidate our definition of value? Not at all. Each is free to render his services only on such terms as are agreeable to himself. If these conditions are made easy, or if none are stipulated for, what is the consequence? The ‹service›, preserving its utility, loses its value. The old priest is persuaded that his services will find their reward in another world, and he cares not for their being recompensed here below. He feels, no doubt, that he is rendering a service to his auditors in addressing them, but he also feels that they do him a service in listening to him. Hence it follows that the transaction is based upon advantage to one of the contracting parties, with the full consent of the other. That is all. In general, exchanges are determined and estimated by reference to self-interest; but, thank God, that is not always the case: they are sometimes based on the principle of sympathy, and in that case we either transfer to another a satisfaction which we might have reserved for ourselves, or we make an effort for him which we might have devoted to our own profit and advantage. Generosity, devotion, self-sacrifice, are impulses of our nature, which, like many other circumstances, influence the actual ‹value› of a particular service, but they make no change on the general law of ‹values›. In contrast to this consoling example, I might adduce another of a very opposite character. In order that a service should possess value, in the economical sense of the word, it is not at all indispensable that it should be a real, conscientious, and useful service; it is sufficient that it is accepted, and paid for by another service. The world is full of people who palm upon the public services of a quality more than doubtful, and make the public pay for them. All depends on the ‹judgment› which we form in each case; and this is the reason why morals will be always the best auxiliary of Political Economy.