Impossible contract refers to a contract that the law will not enforce because there is no feasible way for one of the parties to perform. Impossible contracts include facts or circumstances that excuse performance because the subject or means of performance has deteriorated, has been destroyed, or is no longer available; the method of delivery or payment has failed; a law now prevents performance; or death or illness prevents performance.
Increased or unexpected difficulty and expense cannot be considered as an impossibility and thus do not excuse performance. This is also termed as impossibility of performance. For example, if Hannah contracts to pay John $2000 to paint her house on October 1, but the house burns to the ground before the end of September, Hannah is excused from her duty to pay John the $2000, and John in turn is excused from his duty to paint her house; however, John may still be able to sue for the unjust enrichment of any benefit conferred on Hannah before her house burned down (e.g. if Hannah paid John in advance, then the amount of payment might be a compensatory injury).