Where a contract has no force majeure clause, three common law doctrines may excuse performance. All are narrow.

Impossibility. Performance has become objectively impossible — destruction of the subject matter, death of a person essential to performance, or supervening illegality. Subjective inability, including insolvency, does not qualify.

Impracticability. Performance is possible but only at excessive and unreasonable cost, following an event the non-occurrence of which was a basic assumption of the contract. Courts apply a demanding standard; cost increases of substantial magnitude have been held insufficient where the risk was foreseeable.

Frustration of purpose. Performance remains possible but the event has destroyed the value of the exchange for one party, where the frustrated purpose was known to both and was a basic assumption. The classic examples involve venues rendered useless for the purpose for which they were hired.

Common limits. The party seeking relief must not have caused the event, must not have assumed the risk expressly or by implication, and the event must not have been reasonably foreseeable.

Consequence. Discharge of the contract rather than damages, with restitution of benefits conferred. Partial relief is generally unavailable, which is why an express clause providing for suspension is preferable to reliance on these doctrines.