The doctrine of impracticability in the common law of contracts excuses performance of a duty, where that duty has become unfeasibly difficult or expensive for the party who was to perform.Impracticability is similar in some respects to the doctrine of impossibility because it is triggered by the occurrence of a condition which prevents one party from fulfilling the contract. The major difference between the two doctrines is that while impossibility excuses performance where the contractual duty cannot physically be performed, the doctrine of impracticability comes into play where performance is still physically possible, but would be very burdensome for the party whose performance is due. Thus, impossibility is an objective condition, whereas impracticability is a subjective condition for a court to determine.Typically, the test U.S. courts use for impracticability is as follows (with a few variations among different jurisdictions):