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.
[3] As to whether the non-existence of the subject matter of a contract constitutes (initial) impossibility of performance, see McRae v Commonwealth Disposals Commission.
[6] The English case that established the doctrine of impossibility at common law is Taylor v Caldwell.
[9] At common law, for the defence 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, in the United States 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.