An unforeseen difficulty arising after a contract is made may be resolved by an accord and satisfaction, too. Difficulties that no one could foresee can sometimes serve as catalyst for a further promise that may appear to be without consideration but that the courts will enforce nevertheless. Suppose Peter contracts to build Jerry a house for $390,000. While excavating, Peter unexpectedly discovers quicksand, the removal of which will cost an additional $10,000. To ensure that Peter does not delay, Jerry promises to pay Peter $10,000 more than originally agreed. But when the house is completed, Jerry reneges on his promise. Is Jerry liable? Logically perhaps not: Peter has incurred no legal detriment in exchange for the $10,000; he had already contracted to build the house. But most courts would allow Peter to recover on the theory that the original contract was terminated, or modified, either by mutual agreement or by an implied condition that the original contract would be discharged if unforeseen difficulties developed. In short, the courts will enforce the parties’ own mutual recognition that the unforeseen conditions had made the old contract unfair. The parties either have modified their original contract (which requires consideration at common law) or have given up their original contract and made a new one (called a novation).
It is a question of fact whether the new circumstance is new and difficult enough to make a preexisting obligation into an unforeseen difficulty. Obviously, if Peter encounters only a small pocket of quicksand—say two gallons’ worth—he would have to deal with it as part of his already-agreed-to job. If he encounters as much quicksand as would fill an Olympic-sized swimming pool, that’s clearly unforeseen, and he should get extra to deal with it. Someplace between the two quantities of quicksand there is enough of the stuff so that Peter’s duty to remove it is outside the original agreement and new consideration would be needed in exchange for its removal.