Impracticability (contract law) (See Also: Contractual Duty, Impossibility, Frustration of purpose, Class Action, Force Majeure) = in common law, when a party is unable to perform its contractual obligations, because of an unexpected occurrence that makes those obligations extremely difficult or expensive to fulfil, impracticability can be used as a defence.
US Courts have developed a three-part test to decide on commercial impracticability:
1) The occurrence of an event unexpected at the time when the contract was drafted;
2) The occurrence of the event must result in making a certain performance of the contract extremely difficult or expensive;
3) The parties could not have foreseen the occurrence of the event.
Impracticability is also used as one of the grounds for permitting a Class Action by a large number of persons, when joinder would be impractical.
Force Majeure (Latin: Vis Major): An unexpected and uncontrollable event or circumstance, described legally by the term “act of God”, that prevents the parties of a contract from fulfilling their obligations. In practice, such events usually don't excuse the parties entirely, but only during the period of effect of the force majeure. Force majeure is a clause more common in civil law contracts.
https://www.law.cornell.edu/ucc/2/2-615 - Section 2-615 of the USA Uniform Commercial Code [English]
http://www.legislation.gov.uk/ukpga/Geo6/6-7/40 - UK Frustrated Contracts Act 1943 ([English]
http://law.justia.com/cases/federal/district-courts/texas/txsdce/4:2007cv01919/511172/66/ - Petroworks SA v. Rollings, (S.D. Tex. 2009) (US District Court Southern District of Texas)
http://www.casebriefs.com/blog/law/contracts/contracts-keyed-to-farnsworth/basic-assumptions-mistakes-impracticability-and-frustration/transatlantic-financing-corporation-v-united-states/ - Transatlantic Financing Corp. v. United States, (D.C. Cir., 1966)
https://www.pillsburylaw.com/siteFiles/Publications/BylinedArticleForceMajeureinTumultuousTimesJournalofWorldInvestmentTrade031312.pdf - Augenblick F.; Rousseau A., 2012, Force Majeure in Tumultuous Times: Impracticability as the New Impossibility, The Journal of World Investment & Trade 13 [English]
https://law.stanford.edu/publications/doctrine-of-commercial-impracticability-in-a-second-best-world/ - Sykes A. O., 1990, Doctrine of Commercial Impracicability in a Second-Best World, Journal of Legal Studies 43 [English]
http://www.kentlaw.edu/faculty/rwarner/classes/contracts/impracticability_frustration_mis.html - Warner R., 2003, Summary of impracticability, frustration, and mistake, Chicago- Kent College of Law [English]
Beatson J., 2002, Anson's Law of Contract, United Kingdom, Oxford University Press [English]