Contract Law
Mistake in Contract Law
Apply Sections 20 to 22 to bilateral mistake, unilateral mistake and mistake of law, with categories, effects and leading cases.
The short answer
A bilateral mistake about an existing fact essential to the agreement makes it void, while unilateral mistake ordinarily does not.
The Section 20 test
Use all four steps. A mistake that fails any one of them does not make the agreement void under Section 20.
Both parties mistaken
The error must affect both parties. They may share the same false assumption, or their different understandings may reveal that they were never ad idem on an essential matter.
Matter of fact
The mistake must concern fact, not merely a misunderstanding of Indian law. Foreign law is treated as fact under Section 21.
Existing when agreement formed
Section 20 deals with the factual basis at formation. A later event belongs to impossibility, risk allocation or breach, not formation mistake.
Essential to the agreement
The error must remove or fundamentally alter the basis of the bargain. It is not enough that the truth would merely have affected price or convenience.
Value alone
An erroneous opinion about value is not by itself a mistake of essential fact.
Mistake about the subject matter
The traditional categories are useful only when they help decide whether the fact was truly essential.
Existence
Both parties contract on the assumption that identified goods, property or rights exist, although they had already ceased to exist or never existed.
Identity
The parties attach materially different meanings to the subject, as with two ships or parcels bearing the same description, and the ambiguity cannot be objectively resolved.
Title or ownership
A bargain may fail where both parties wrongly assume that one has a transferable right, although the other already owns it or the assumed right does not exist.
Quantity
A shared error about area, amount or unit can be essential where the bargain and price were built on that basis.
Quality
Quality mistake must be fundamental, making the thing essentially different from what both parties believed. A defect that merely changes market value is ordinarily insufficient.
Common assumption and mutual misunderstanding
Both can fall within Section 20, but the reasoning is different.
In a common mistake, both parties make the same false assumption, such as believing that specific goods still exist. In a mutual misunderstanding, each party attaches a different meaning to an essential expression, so objective consensus may be absent.
Before declaring the agreement void, interpret the words and surrounding circumstances objectively. If the contract itself allocates the relevant risk, a party cannot use mistake simply because that risk later produces a bad result.
Mistake of law under Section 21
The Act draws a direct distinction between Indian law and foreign law.
Indian law
A contract is not voidable merely because a party misunderstood a law in force in India. Parties are ordinarily taken to know the governing domestic law.
Foreign law
The content of foreign law must be proved as fact. A shared essential mistake about it is therefore tested through Section 20.
Fact and law can overlap
Identify what exactly was mistaken. A party may know the legal rule but be mistaken about a factual status on which the rule operates.
Unilateral mistake under Section 22
One party cannot ordinarily escape a contract merely because that party misunderstood the facts.
General rule
Section 22 says the contract is not voidable merely because one party was under a mistake of fact.
Identity cases
A serious mistake about the other party's identity may prevent agreement where identity, not merely creditworthiness, was essential and the apparent acceptance was not directed to the actual person.
Character of document
Where a person signs something fundamentally different from the document believed to be signed, the issue may be absence of consent to that transaction. Mistake about contents ordinarily has a different effect.
Known mistake
If one party knows that the other is using an essential term in a different sense, ordinary objective agreement may be absent. This is not a broad equitable power to correct every one-sided error.
Effect of mistake and restoration
Section 20 makes the agreement void, not merely voidable at one party's option.
No party can enforce a promise that forms part of the void agreement. A forfeiture or penalty clause within it ordinarily falls with the agreement unless a genuinely separate agreement survives.
Where an advantage was received under an agreement later discovered to be void, Section 65 may require restoration. The remedy prevents one party from retaining the benefit of a bargain that Section 20 treats as legally ineffective.
Leading cases and what they establish
Read each authority for the proposition it proves, the legal question it answers and the reasoning that supports the result.
Raffles v. Wichelhaus
(1864) 2 H&C 906
Held: A latent ambiguity about the subject of the bargain can prevent consensus where each party reasonably means a different thing.
Why it matters: Use it for mistake or ambiguity concerning identity of the subject matter.
Couturier v. Hastie
(1856) 5 HL Cas 673
Held: A bargain made on the shared basis that identified goods existed failed when the goods had already ceased to exist in the contemplated form.
Why it matters: Use it for common mistake about the existence of specific subject matter, while checking the actual risk allocated by the contract.
Tarsem Singh v. Sukhminder Singh
(1998) 3 SCC 471
Held: A material shared mistake about the basis on which land and price were calculated made the agreement void under Section 20.
Why it matters: Use it for bilateral mistake about an essential quantity or basis of a property transaction.
Read the judgmentNingawwa v. Byrappa
AIR 1968 SC 956
Held: The Supreme Court distinguished fraud as to the character of a document, which can negate the transaction itself, from fraud as to its contents, which ordinarily makes it voidable.
Why it matters: Use it cautiously when a unilateral document mistake is really a question whether consent to that kind of transaction existed at all.
Read the judgmentUsing this topic in a legal answer
A clear answer sequence
- Classify the mistake as fact or law, bilateral or unilateral.
- For Section 20, prove both parties, existing fact and essentiality separately.
- Identify the category of mistake and ask whether the contract allocated that risk.
- Exclude a mere error of value, quality or future expectation.
- Apply Sections 21 or 22 and analyze real consent in any narrow identity or document case.
- State the effect and consider restoration under Section 65.
Points that are often confused
- Treating every bad bargain as mistake.
- Forgetting that Section 20 requires both parties to be mistaken.
- Calling a mistaken prediction an existing fact.
- Listing identity and quality as automatic grounds without proving essentiality.
- Describing a Section 20 agreement as voidable instead of void.
Open the revision and self-check sheet
Rules to retain
- Section 20 requires both parties, fact, existing mistake and essentiality.
- Common mistake means one shared false assumption.
- Mutual mistake can reveal two different meanings and no consensus.
- Value alone is expressly excluded by Section 20.
- Mistake of Indian law gives no ordinary relief.
- Foreign law is treated as fact.
- Unilateral mistake ordinarily does not invalidate the contract.
- Section 65 may restore benefits received under an agreement discovered to be void.
Questions to test understanding
- What four points must be shown under Section 20?
- How is foreign law treated?
- Does a mistaken opinion about value make an agreement void?
Questions students ask
Does every factual mistake make an agreement void?
No. Under Section 20, both parties must be mistaken about a fact essential to the agreement.
What happens if only one party is mistaken?
Section 22 says the contract is not voidable merely for unilateral mistake, though narrow cases involving absence of real consent may require separate analysis.
Is a wrong estimate of value a bilateral mistake?
No. Section 20 expressly says that an erroneous opinion about value is not itself a mistake of fact essential to the agreement.
What is the difference between mistake and frustration?
Mistake concerns the essential factual basis when the agreement is formed. Frustration under Section 56 concerns a supervening event that later makes performance impossible or unlawful.
Can money paid under a void agreement be recovered?
Section 65 may require restoration where an agreement is discovered to be void. Tarsem Singh applied this principle to refund earnest money after a Section 20 mistake.
Is mistake about foreign law treated like Indian law?
No. Section 21 treats mistake about foreign law in the same way as mistake of fact, while mistake about Indian law does not ordinarily make a contract voidable.
Primary sources and further reading
- Indian Contract Act, 1872 on India Code
- Tarsem Singh v. Sukhminder Singh, Supreme Court of India
- Ningawwa v. Byrappa, Supreme Court of India
This article is written for legal education. Verify the governing provision, applicable amendments and complete judgment before relying on a proposition in practice.