preexisting duty rule
preexisting-duty rule. Contracts. The rule that if a party does or promises to do what the party is already legally obligated to do — or refrains or promises to refrain from doing what the party is already legally obligated to refrain from doing — the party has not incurred detriment. • This rule’s result is that the promise does not constitute adequate consideration for contractual purposes. For example, if a builder agrees to construct a building for a specified price but later threatens to walk off the job unless the owner promises to pay an additional sum, the owner’s new promise is not enforceable because, under the preexisting-duty rule, there is no consideration for that promise. — Also termed preexisting-legal-duty rule. [Cases: Contracts 75. C.J.S. Contracts § 120.]
