preexisting duty rule
- A principle in contract law which states that if a party promises to perform a duty that they're already obligated to perform under an existing agreement, it cannot be considered a valid consideration for changing the terms of the contract
- According to the preexisting duty rule, the car mechanic could not demand an extra fee for repairing the engine, since it was part of his original contract.
- The preexisting duty rule was applied to dismiss the tenant's claim for a rent reduction, as the landlord was already obligated to provide maintenance under the initial contract.
- Per the preexisting duty rule, the teacher's promise to offer extra tutoring, a duty already within his contract, could not serve as valid consideration for a raise.