In law a formal agreement recognized as constituting an obligation to do or not to do a particular thing. Both Bible (Prov. vi. 1-5; perhaps also Deut. xxiii. 23 and Ps. xv. 4) and Mishnah (B. M. iv. 2) attach great sacredness to a promise, and rebuke a breach of promise, even where the courts of law can not enforce its observance. From the above-cited passage in Proverbs and from other passages in the same book, it seems that at one time "striking hands" over a promise, like the "Handschlag" in German law, gave special force in the courts to a promise or contract. In the Talmud this ceremony carries only a moral or religious sanction. There is no one word, either in Bible or in Mishnah, which, like the Latin "contractus" or "pactum," or the English "contract," covers all agreements from which a liability or change of rights may arise. Different kinds of contracts, whether executed or executory, are denoted by their own special names. As to some of these the article on Deed may be consulted; in which article it also appears that greater force is given to a contract by the formality of drawing it up in writing and by having it attested by two competent witnesses. In the article Alienation and Acquisition it has been shown that the executed contract of sale, conveyance, or gift can take effect only by the actual delivery of an article, and not by the assent of the parties alone.

An undertaking, in the course of judicial proceedings, to pay a stated sum—for instance, an undertaking by a friend of the defendant to become surety for him in order to postpone execution on a judgment—has in all respects the same force as an attested bond (this doctrine is deduced by the codifiers from Mish. B. B. x. 8; see references in "Be'er ha-Golah" to Shulḥan 'Aruk, Ḥoshen Mishpaṭ, 129, 6); just as in common law a recognizance in court becomes a "debt by specialty" as much as a bond under seal.

The law, written or oral, has established certain rules which govern the ordinary relations of life and the contracts growing out of them; such as the relations between the owner and bailor, and the bailee or keeper of goods (see Bailments). In most cases it is competent for the parties to change the implied rules by express contract. He who exacts or stipulates for such special terms is called "matneh" (V04p249001.jpg), and while the Mishnah (B. M. vii. 11) lays down the rule, "Whoever stipulates against what is written in the Torah finds his terms void," this is but one of those opinions of R. Meïr which form the undistinguished text of the Mishnah, but are not always good law; while, according to the Gemara (B. M. 94a), the opinion of his contemporary, R. Judah ben 'Illai, prevailed; viz., that in mere matters of money, stipulations contrary to the Torah were admissible. In the case of marriage it seems that all are agreed that a stipulation not to pay the wife the minimum of a jointure in case of the husband's death, or of divorce, being altogether contrary to the policy of the Law and to the dignity of the daughters of Israel, must be deemed void as well as immoral (see Ketubah). A contract for the payment to a fellow Jew of interest on a loan is, of course, void; for the Mosaic law forbids by its own terms the debtor's promise as well as the creditor's exaction of interest. For like reasons, it seems that an agreement to keep alive a debt (at least one arising from a loan) beyond the year of release would have been deemed ineffectual but for Hillel's institution ("taḳḳanah") of the Prosbul.

The rule as to conditions precedent, found in the same section of the Mishnah, has, at the end of the article on Alienation, been explained by a quotation from Maimonides applicable to cases where the fulfilment of the condition is to lead to the transfer of property. The Shulḥan 'Aruk (Ḥoshen Mishpaṭ, 207, 11, 12) shows how in other cases promises to take effect upon the fulfilment of a future condition are ineffectual, even where the promisor, to give effect to his promise concerning a bond or deed, puts it into the hands of a trustee ("shalish"). It seems to have been the policy of the sages to exclude everything like complication in contractual dealings between man and man.

Under the Jewish law an executory contract had to rest upon a consideration; but this need not go to the personal benefit of the obligor. There is a consideration for the promise of the surety, in a loan or forbearance given to the principal debtor, provided the surety binds himself at the time the debtor receives the benefit (see Deed, referring to B. B. x. 8); while a subsequent promise by the surety would be without consideration (see Asmakta).

But while, generally speaking, a consideration is necessary to support a promise, a person may, with his eyes open, bind himself by bond, or by a promise in the presence of witnesses, to pay to another a sum of money, though he does not owe him anything whatever, just as he may make to another a deed of gift of land; which principle is derived from B. B. 149a, "to acquire by acknowledgment," and from Ket. 101b (see Maimonides, "Yad," Mekirah, xi.; also Shulḥan 'Aruk, Ḥoshen Mishpaṭ, 40). But where the bond or promise is made under a mistaken belief by the obligor that he owes, or is liable for, the sum named (see, for an illustration, Ḥoshen Mishpaṭ, 126, 3), such bond or promise may be avoided upon a showing of the true facts and of the mistake committed, just as a mistaken purchase may be set aside. For, as at common law "fraud vitiates everything," so, to a great extent, does mistake.

Where a contract is made on a Sabbath or a day of festival, although the parties should be punished for breaking the custom which forbids trading on the Sabbath and on festivals, yet the contract is good; for the act giving effect to it, such as the handling or moving of a bought chattel, or occupancy of a bought parcel of land by the purchaser, is not generally a breach of the Sabbath under the Mosaic law; and, after the day closes, the contract may be reduced to writing (Mekirah, xxx. 7; Ḥoshen Mishpaṭ, 235, 28).

For different kinds of contracts see Alienation and Acquisition; Bailments; Broker; Deed; Loans; Master and Servant; Suretyship.