Contract law (2022): Excuses for non-performance: Impossibility + Frustration of purpose

In contract law, impossibility is an excuse for the nonperformance of duties under a contract, based on a change in circumstances (or the discovery of preexisting circumstances), the nonoccurrence of which was an underlying assumption of the contract, that makes performance of the contract literally impossible.

For example, if Ebenezer contracts to pay Erasmus £100 to paint his house on October 1, but the house burns to the ground before the end of September, Ebenezer is excused from his duty to pay Erasmus the £100, and Erasmus is excused from his duty to paint Ebenezer's house; however, Erasmus may still be able to sue under the theory of unjust enrichment for the value of any benefit he conferred on Ebenezer before his house burned down.

The parties to a contract may choose to ignore impossibility by inserting a hell or high water clause, which mandates that payments continue even if completion of the contract becomes physically impossible.

In common law, for the defense of "impossibility" to be raised performance must not merely be difficult or unexpectedly costly for one party, there must be no way for it to actually be accomplished; however, it is beginning to be recognized that "impossibility" under this doctrine can also exist when the contemplated performance can be done but only at an excessive and unreasonable cost, i.e., commercial impracticability. On the other hand, some sources see "impossibility" and impracticability as being related but separate defenses.

The English case that established the doctrine of impossibility at common law is Taylor v Caldwell.

Frustration of purpose, in law, is a defense to enforcement of a contract. Frustration of purpose occurs when an unforeseen event undermines a party's principal purpose for entering into a contract such that the performance of the contract is radically different from performance of the contract that was originally contemplated by both parties, and both parties knew of the principal purpose at the time the contract was made. Despite frequently arising as a result of government action, any third party or even nature can frustrate a contracting party's primary purpose for entering into the contract. The concept is also called commercial frustration.

For example, if Joe gets a mortgage for a new home, suppose after three years, the home is destroyed, through no fault of Joe's. Without a hell or high water clause, Joe might be exempt from the remainder of the mortgage, as the principal purpose of the contract, to have a home to live in, has been compromised. However, he might still have a foreclosure on his credit rating.

Frustration of purpose is often confused with the closely related doctrine of impossibility. The distinction is that impossibility concerns the duties specified in the contract, but frustration of purpose concerns the reason a party entered into the contract. An example is if entrepreneur Emily leases space from landlord Larry so that she can open a restaurant that serves only Tibetan Speckled Lizard meat. If the city rezones the property to forbid commercial uses or if the property is destroyed by a tornado, both Larry and Emily are excused from performing the contract by impossibility.