Section Iv.--_of Contracts_.

1. A contract is a bargain productive of an obligation of commutative justice in each of the contracting parties. A bargain is a consent of two wills to the same object. Thus a promise, before it is accepted, is not a bargain. But even after acceptance a promise is not a contract, for the promiser may not choose to bind himself in justice, but only in good faith, while the promisee is under no obligation whatever.

2. There are such things as implicit contracts, attached to the bearing of certain offices, whereby a man becomes his brother's keeper. The liability contracted is limited by the nature of the office: thus a physician is officially bound in justice as to his patient's pulse, but not officially as to his purse. Where there is no explicit contract, the duties which the subjects of a person's official care have towards him are not duties of commutative justice. Thus these implicit contracts are not strictly contracts, as failing to carry a full reciprocity.

3. Contracts are either consensual or real, according as they are either complete by the mere consent of the parties, or further require that something should change hands and pass from one to the other. What contracts are consensual, and what real, depends chiefly on positive law. No natural law can tell whether buying and selling, for instance, be a consensual or a real contract. The interest of this particular case is when the goods are lost in transmission: then whichever of the two parties at the time be determined to be the owner, apart from culpable negligence or contrary agreement of the sender, he bears the loss, on the principle, res perit domino.

4. Contracts are otherwise divided as onerous and gratuitous. In an onerous contract either party renders some advantage in return for the advantage that he receives, as when Titius hires the horse of Caius. In a gratuitous contract all the advantage is on one side, as when Titius does not hire but borrows a horse. The Roman lawyers further distinguish contracts, somewhat humorously, into contracts with names and contracts without names, or nominate and innominate, as anatomists name a certain bone the innominate bone, and a certain artery the innominate artery. Innominate contracts are reckoned four: I give on the terms of your giving, otherwise than as buying and selling,--to some forms of this there are English names, as exchange and barter: I do on the terms of your doing: I do on the terms of your giving: I give on the terms of your doing.

Readings.--De Lugo, De Just. et Jure, 22, nn. 1, 2, 5, 6, 9, 16, 17. For buying and selling and the frauds incident thereto, Paley, Moral Philosophy, bk. iii., p. 1, c. vii.