Contract

A contract is any legally-enforceable promise or set of promises made between parties. In the civil law, contracts are considered to be part of the general law of obligations. This article describes the law relating to contracts in common law jurisdictions.

Bilateral v. unilateral contracts

Contracts may be bilateral or unilateral. The more common of the two, a bilateral contract, is an agreement in which each of the parties to the contract makes a promise or promises to the other party. For example, in a contract for the sale of a home, the buyer promises to pay the seller £200,000 in exchange for the seller's promise to deliver title to the property.

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In a unilateral contract, only one party to the contract makes a promise. A typical example is the reward contract: A promises to pay a reward to B if B finds A's dog. B is not obliged to find A's dog, but A is obliged to pay the reward to B if B finds the dog. In this example, the finding of the dog is a condition precedent to A's obligation to pay.

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An offer of a unilateral contract may often be made to many people (or 'to the world') by means of an advertisement. In that situation, acceptance will only occur on satisfaction of the condition (such as the finding of the offeror's dog). If the condition is something that only one party can perform, both the offeror and offeree are protected — the offeror is protected because he will only ever be contractually obliged to one of the many offerees; and the offeree is protected, because if she does perform the condition, the offeror will be contractually obliged to pay her.

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In unilateral contracts, the requirement that acceptance be communicated to the offeror is waived. The offeree accepts by performing the condition, and the offeree's performance is also treated as the price, or consideration, for the offeror's promise.

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The most common type of unilateral contract is the insurance contract. The insurance company promises to pay the insured a stated amount of money on the happening of an event if the insured pays premiums; note that the insured does not make any promise to pay the premiums.

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Courts generally favor bilateral contracts. The general rule in the United States is: "In case of doubt, an offer is interpreted as inviting the offeree to accept either by promising to perform what the offer requests or by rendering the performance, as the offeree chooses." Restatement (Second) of Contracts § 32 (1981) (emphasis added). Here the law attempts to provide some protection from the risk of revocation in a unilateral contract to the offeree. Note that if the offer specifically requests performance rather than a promise, a unilateral contract will exist. See option contracts for more information on protection given to the offeree in a unilateral contract.

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