Non est factum

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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 B in Canadian contract law6
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

Non est factum (Latin for "it is not [my] deed") is a defence in contract law that allows a signing party to escape performance of an agreement "which is fundamentally different from what he or she intended to execute or sign".^[1] A claim of non est factum means that the signature on the contract was signed by mistake, without knowledge of its meaning. A successful plea would make the contract void ab initio.^[2]

According to Saunders v Anglia Building Society [1971] AC 1004,^[3] applied in Petelin v Cullen [1975],^[2] the strict requirements necessary for a successful plea are generally that:

• The person pleading non est factum must belong to "class of persons, who through no fault of their own, are unable to have any understanding of the purpose of the particular document because of blindness, illiteracy or some other disability".^[1] The disability must be one requiring the reliance on others for advice as to what they are signing.^[1][2]
• The "signatory must have made a fundamental mistake as to the nature of the contents of the document being signed", including its practical effects.^[1]
• The document must have been radically different from one intended to be signed.^[1]

Non est factum is difficult to claim as it does not allow for negligence on the part of the signatory; i.e. failure to read a contract before signing it, or carelessness,^{[2]: para 12} will not allow for non est factum. Furthermore, the Court has noted that there is a heavy onus that must be discharged to establish this defence as it is an "exceptional defence".^{[1][2]: 359–60}