An agreement formed by an exchange of a promise in which the promise of one party is consideration supporting the promise of the other party.
A bilateral contract is distinguishable from a unilateral contract, a promise made by one party in exchange for the performance of some act by the other party. The party to a unilateral contract whose performance is sought is not obligated to act, but if he or she does, the party that made the promise is bound to comply with the terms of the agreement. In a bilateral contract both parties are bound by their exchange of promises.
Both parties to a bilateral contract make promises. With respect to the promise in issue, the party making the promise is the promisor and the other party is the promisee. The legal detriment incurred by the promisee consists of a different promise by him or her to do something or refrain from doing something that he or she was not previously legally obligated to do or to refrain from doing. This legal detriment constitutes consideration, the cause, motive, or benefit that induces one to enter into a contract. Consideration is an essential component of a contract.
Traditionally, courts have distinguished between unilateral and bilateral contracts by determining whether one or both parties provided consideration and at what point they provided the consideration. Bilateral contracts were said to bind both parties the minute the parties exchange promises, as each promise is deemed sufficient consideration in itself. Unilateral contracts are said to bind only the promisor and do not bind the promisee unless the promisee accepts by performing the obligations specified in the promisor's offer. Until the promisee performs, he or she has provided no consideration under the law.
For example, if someone offered to drive you to work on Mondays and Tuesdays in exchange for your promise to return the favor on Wednesdays and Thursdays, a bilateral contract would be formed binding both of you once you provided consideration by accepting those terms. But if that same person offered to pay you $10 each day you drove him to work, a unilateral contract would be formed, binding only upon the promisor until you provided consideration by driving him to work on a particular day.
Modern courts have de-emphasized the distinction between unilateral and bilateral contracts. These courts have found that an offer may be accepted either by a...