MBE Rules · Contracts
Pre-existing duty rule
The rule
Performing or promising to perform a pre-existing legal duty is not consideration. A promise to pay extra for performance the promisee already owes is unenforceable at common law. UCC §2-209(1) abrogates this rule for sale-of-goods modifications.
In plain English
If you promise to do something you already have to do, you can't use that promise to make a new deal.
Worked example
The contractor agrees to finish a house for $10,000. Halfway through, he demands $2,000 more to finish. The homeowner agrees but doesn't have to pay the extra $2,000 because the contractor was already obligated to finish.
Memory hook
Pre-existing duty = no new dough. Doing what you’re already bound to do doesn’t warrant extra pay.
The trap
Students think: Any modification is unenforceable. Wrong, because UCC allows modifications without new consideration for goods. The actual test is common law vs. UCC context.
How examiners test it
The MBE loves: a contractor demands more money mid-project. Trap: students forget UCC allows modifications for goods, but not services. Look for the nature of the contract.
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