Those who write upon the principles of jurisprudence, consider only what the person to whom the obligation is due, ought to think himself entitled to exact by force; what every impartial spectator would approve of him for exacting, or what a judge or arbiter, to whom he had submitted his case, and who had undertaken to do him justice, ought to oblige the other person to suffer or to perform. The casuists, on the other hand, do not so much examine what it is, that might properly be exacted by force, as what it is, that the person who owes the obligation ought to think himself bound to perform from the most sacred and scrupulous regard to the general rules of justice, and from the most conscientious dread, either of wronging his neighbour, or of violating the integrity of his own character. It is the end of jurisprudence to prescribe rules for the decisions of judges and arbiters. It is the end of casuistry to prescribe rules for the conduct of a good man. By observing all the rules of jurisprudence, supposing them ever so perfect, we should deserve nothing but to be free from external punishment. By observing those of casuistry, supposing them such as they ought to be, we should be entitled to considerable praise by the exact and scrupulous delicacy of our behaviour. It may frequently happen that a good man ought to think himself bound, from a sacred and conscientious regard to the general rules of justice to perform many things which it would be the highest injustice to extort from him, or for any judge or arbiter to impose on him by force. To give a trite example; a highwayman, by the fear of death, obliges a traveller to promise him a certain sum of money. Whether such a promise, extorted in this manner by unjust force, ought to be regarded as obligatory, is a question that has been very much debated. If we consider it merely as a question of jurisprudence, the decision can admit of no doubt. It would be absurd to suppose that the highwayman can be entitled to use force to constrain the other to perform. To extort the promise was a crime which deserved the highest punishment, and to extort the performance would only be adding a new crime to the former. He can complain of no injury who has been only deceived by the person by whom he might justly have been killed. To suppose that a judge ought to enforce the obligation of such promises, or that the magistrate ought to allow them to sustain an action at law, would be the most ridiculous of all absurdities. If we consider this question, therefore, as a question of jurisprudence, we can be at no loss about the decision.