What is the single mistake rule?

Asked by: Asia Wuckert  |  Last update: January 31, 2026
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The "single mistake rule" generally refers to a legal doctrine in contract law, specifically regarding unilateral mistake, where a contract may be voidable if one party makes a mistake and the other party knew or should have known about it. It is distinct from "mutual mistake," where both parties are mistaken.

What are the three types of mistakes in contract law?

Common law has identified three different types of mistake in contract: the 'unilateral mistake', the 'mutual mistake', and the 'common mistake'. The distinction between the 'common mistake' and the 'mutual mistake' is important.

What is the honest mistake rule?

If a defendant has an honest and reasonable mistake of fact regarding their behavior or actions, they may not have the required criminal intent to be held criminally liable.

What is the single meaning rule in defamation?

The Single Meaning Rule

In a defamation claim, a publication is not assessed through the myriad interpretations different readers might have. Instead, the law applies the single meaning rule: the court fixes on one meaning as the “right” meaning for legal purposes.

What is the rule for unilateral mistake?

A party to a contract is entitled to reformation of the contract based on one party's unilateral mistake only if the other party engaged in inequitable conduct. A party acts inequitably if it knowingly conceals a material fact from the other party and has a duty to disclose that knowledge to the other party.

This One Mistake Is Ruining Your First Meal | Dr. Mandell

28 related questions found

What are the three types of mistakes?

There are three broad categories of mistake which this chapter will explore:

  • Non-Agreement mistake.
  • Mutual agreement mistake.
  • Unilateral mistake.

What is Section 22 of the contract Act?

Contract caused by mistake of one party as to matter of fact. — A contract is not voidable merely because it was caused by one of the parties to it being under a mistake as to a matter of fact.

What are the 4 things to prove defamation?

The four core elements of defamation are: a false statement presented as fact, publication (communication) to a third party, fault (at least negligence) by the speaker, and resulting damages or harm to the plaintiff's reputation. Proving these elements is necessary to establish a successful defamation claim, whether it's libel (written) or slander (spoken). 

How hard is it to win a defamation lawsuit?

There are several key elements of defamation that need to be established and proven to win your defamation lawsuit. Winning a defamation lawsuit requires thorough evidence, legal expertise, and a strong argument to prove the elements necessary to establish your case.

Can normal people sue for defamation?

A plaintiff who is a public official or public figure must prove that you published the statement with “actual malice,” a higher level of fault, while a plaintiff who is a private individual generally must prove that you acted negligently, a lower level of fault.

What evidence is needed to prove a fact mistake?

Statutory requirement: The underlying crime must include a mental-state element (e.g., intent, knowledge). Honest belief: The defendant must have genuinely believed in the mistaken fact. Reasonableness: The belief must be what a reasonable person in the same circumstances would have thought.

How to prove intent to deceive?

To prove intent to deceive, a plaintiff must show that the defendant knowingly made false statements, concealed material facts, or acted with reckless disregard for the truth, leading to the plaintiff's reliance and financial harm.

What are four types of mistakes that can invalidate a contract?

However, being aware of the four vices that can void a contract — duress, undue influence, misrepresentation, and mistake — is crucial for ensuring that your agreements are legally enforceable and that your rights are protected.

Which is the most significant violation of a contract?

Material breach.

Sometimes referred to as a total breach, a material breach is considered the most serious because one party failed to perform the duties detailed in the contract. Thus, the breach is so significant, the purpose of the agreement is determined to be completely broken.

What is the common mistake law?

Common mistake (where the mistake is shared by both parties, is fundamental and directly affects the basic definition of what the parties are contracting for). The mistake will render the contract void if it robs it of all substance. Mutual mistake (where the parties are at cross-purposes with one another).

What are the 4 breaches of contract?

The four main types of breach of contract are Material Breach (a major violation), Minor Breach (a trivial failure), Anticipatory Breach (a warning sign of future non-performance), and Actual Breach (a failure to perform when due), with some systems also identifying a more severe Fundamental Breach, but these four provide the core framework for understanding contract violations and their consequences.
 

What is proof of slander?

To prove slander (spoken defamation), you must show the defendant made a false statement of fact, communicated it to a third party, did so with at least negligence or actual malice, and that it caused you actual harm or damages, like financial loss, with truth being a complete defense. Evidence often includes witnesses, recordings, and financial records to prove the statement's falsehood, publication, and resulting damages.
 

How much money does it take to sue someone for defamation?

Suing for defamation is often costly. Legal fees typically range from tens of thousands of dollars for straightforward cases to well over $100,000 for complex trials. The exact cost depends on case complexity, evidence and how far the case proceeds. Simple cases may cost tens of thousands of dollars.

How to deal with someone defaming you?

To handle slander, you can calmly address the person directly (if safe), build a support network of allies, focus on your integrity and positive actions, document everything, and, if necessary, consult a lawyer for formal steps like cease and desist letters or legal action, especially if the slander impacts your job or reputation significantly.
 

What are the emotional distress damages in defamation?

This harm can manifest in various ways, including anxiety, depression, humiliation, and loss of sleep. To successfully claim emotional distress in a defamation case, plaintiffs typically need to demonstrate: Severity of Distress: The emotional distress must be significant. Minor or fleeting discomfort is insufficient.

Is it worth suing someone for defamation?

Suing for defamation can be worthwhile if you suffered significant, measurable harm (reputational, financial, emotional) from false statements, and you have strong evidence, but it's a difficult, costly process involving intrusive discovery and proving damages, making legal consultation essential to weigh potential recovery against high legal fees and stress. 

How much evidence do you need for defamation?

The burden of proof is upon the Claimant. To prove defamation, you need to establish that: The statement made against you is not substantially true. The statement was made knowingly or recklessly.

What is Section 69 of the contract?

Section 69 provides that if a person pays a debt or obligation that another is legally bound to pay, and the payer is "interested" in the fulfillment of that obligation, then the payer is entitled to reimbursement from the person who was originally responsible.

What is the doctrine of unilateral mistake?

Unilateral Mistake

In unilateral mistake cases, only one party is mistaken: the other party knows about it and takes advantage of the error. So, it's not a mistake made by both parties to a contract. In Hartog v Colin and Shields (1939) the seller had made a mistake as to the price of goods.

What is Article 22 of the Basic law?

Article 22 No department of the Central People's Government and no province, autonomous region, or municipality directly under the Central Government may interfere in the affairs which the Hong Kong Special Administrative Region administers on its own in accordance with this Law.