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

In the law of contracts, the mirror image rule, also referred to as an unequivocal and absolute acceptance requirement, states that an offer must be accepted exactly with no modifications.^[1] The offeror is the master of their own offer. An attempt to accept the offer on different terms instead creates a counter-offer, and this constitutes a rejection of the original offer.^[2]

England

The English common law established the concepts of consensus ad idem, offer, acceptance and counter-offer. The leading case on counter-offer is Hyde v Wrench [1840].^[3] The phrase "Mirror-Image Rule" is rarely (if at all) used by English lawyers; but the concept remains valid, as in Gibson v Manchester City Council [1979],^[4] and Butler Machine Tool v Excello.^[5]

Australia

This position is adhered to in Australia (New South Wales). If a person were to accept an offer, but make a modification, then they are actually rejecting the offer presented to them and are proposing a counter-offer: Masters v Cameron (1954) 91 CLR 353. That modifying party is then the one making a new offer, and the original offeror is now the one who has to accept.

United States

In the United States, this rule still exists at common law. However, the Uniform Commercial Code ("UCC") dispenses with it in § 2-207 (but it can also be argued that § 2-207(1) enforces the mirror image rule).^[6] Therefore, its applicability depends upon what law governs. Most states have adopted the UCC, which governs transactions in goods. Contracts for services or land, for example, would not be governed by the UCC. The second Restatement of Contracts also provides that when parties have not agreed to an essential term, "a term which is reasonable in the circumstances is supplied by the court." However, it may not be possible for a reasonable term to be supplied by the court.