pre-existing duty doctrine

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The pre-existing duty doctrine is a principle under contract law where if a party to a contract does what they are already obligated to do in exchange for a modification of the contract, the modification will be voidable. Since the party is under a pre-existing duty to perform, the promise to complete their pre-existing duty is not consideration sufficient for the modification of the contract. 

The rule originated in the common law of England and is meant to protect a party from extortion by the other party threatening to not complete their obligation unless the contract is modified. The Uniform Commercial Code §2-209 does away with the pre-existing duty doctrine, allowing modification to a contract to be made without consideration, but the modification must still comply with the other requirements of the UCC. The Second Restatement of Contracts §89 also does away with the pre-existing duty doctrine, provided that the modification is fair and equitable in view of unanticipated circumstances or material change of position in reliance on the promise. Despite this change, many states still follow the common law rule requiring separate consideration to modify a contract.

[Last updated in February of 2024 by the Wex Definitions Team]