Contract law
Formation
Capacity Offer and acceptance Meeting of the minds2 Abstraction principle4,5 Posting rule1 Mirror image rule Invitation to treat Firm offer Consideration1,4 Implication-in-fact Collateral contract
Defences
Misrepresentation Mistake Threats and unequal bargaining power Illegality and public policy Unconscionability Culpa in contrahendo2 Force majeure Frustration of purpose Impossibility Impracticability Hardship Set-off Illusory promise1 Statute of frauds1 Non est factum1 Unclean hands1 Accord and satisfaction1 Exculpatory clause
Interpretation
Parol evidence3 Contract of adhesion Integration clause Contra proferentem UNIDROIT Principles
Dispute resolution
Choice of law clause Forum selection clause Hague Choice of Court Convention Arbitration New York Convention UNCITRAL Model Law Mediation Singapore Mediation Convention Enforcement of foreign judgments Hague Judgments Convention
Rights of third parties
Privity of contract1 Assignment Delegation Novation Third-party beneficiary
Breach of contract
Anticipatory repudiation Cover Exclusion clause Efficient breach Deviation Fundamental breach
Remedies
Specific performance3 Money damages Liquidated, stipulated, or penal damages3 Rescission
Quasi-contractual obligations
Promissory estoppel1 Quantum meruit1 Unjust enrichment Restitution Negotiorum gestio2
Duties of parties
Duty of honest contractual performance (or doctrine of abuse of rights)6 Duty of good faith (also implied covenant of good faith and fair dealing or duty to negotiate in good faith)7 Contract A and Contract B6
Related areas of law
Conflict of laws Commercial law
By jurisdiction
Australia Canada China (mainland) Ireland India Saudi Arabia United Kingdom England and Wales Scotland United States
Other law areas
Tort law Property law Wills, trusts, and estates Criminal law Evidence
Notes
1 Specific to common law jurisdictions 2 Specific to civil and mixed law jurisdictions 3 Historically restricted in common law jurisdictions but generally accepted elsewhere; availability varies between contemporary common law jurisdictions 4 Specific to the German Bürgerliches Gesetzbuch and other civil codes based on the pandectist tradition 5 Explicitly rejected by the UNIDROIT Principles of International Commercial Contracts 6 Specific to Canadian contract law both in Québec and in the country's common law provinces 7 Specific to civil law jurisdictions, the American Uniform Commercial Code, and Canadian jurisprudence in both Québec and the common law provinces pertaining to contractual and pre-contractual negotiation
v t e

The doctrine of impracticability in the common law of contracts excuses performance of a duty, where the said 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 extremely 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):^[1]

1. There must be an occurrence of a condition, the nonoccurrence of which was a basic assumption of the contract,
2. The occurrence must make performance extremely expensive or difficult
3. This difficulty was not anticipated by the parties to the contract (note: some jurisdictions require that there be no measure within the contract itself to allocate risk between the parties)

Restatement of Contracts

Section 261 of the Restatement (Second) of Contracts does not explicitly define the scope of what is considered impracticable, as it is a fairly subjective and fact-intensive test for the courts. Generally, courts do not consider events such as an increase in price or costs beyond a normal range to allow for discharge of duties on grounds of impracticability, as such events are normally foreseeable risks of fixed-price contracts.

Uniform Commercial Code

Section 2-615 of the Uniform Commercial Code deals with impracticability in the context of sales of goods, and introduces some additional constraints on the parties. A party whose ability to perform his obligations has only been partially affected must allocate production and delivery among his customers in a manner which is fair and reasonable, affording each of them with partial performance, and must notify all purchasers that there will be delay, partial delivery, or non-delivery. This is similar in some respects to the doctrine of general average in admiralty law.

According to note 4 under UCC 2–615, increased cost alone does not excuse performance unless the rise in cost is due to some unforeseen contingency which alters the nature of performance. It further explains that a change in market conditions resulting in a rise or drop in prices is not sufficient to claim impracticability because the parties assumed that risk when the contract was made. The comments indicate that contingencies such as war, embargo, crop failures, or a failure of a major source of supply that causes the market change or prevents a seller from obtaining supplies necessary for his performance would justify a claim of impracticability.