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Understanding Unilateral Mistake in Contract Law: Identity and Terms

Question from gskcjjc, Understanding Unilateral Mistake in Contract Law: Identity and Terms

Answer from AI:

In contract law, a unilateral mistake occurs when one party is under a misunderstanding about a fundamental aspect of the contract. This misunderstanding can relate to the identity of the party they are contracting with (mistake as to identity) or the terms of the contract itself (mistake as to terms). Understanding these concepts is crucial for grasping the broader principles of contract law in the UK.

Mistake as to Identity

A mistake as to identity happens when one party enters into a contract under a false impression about who the other party is. This type of mistake can significantly impact the enforceability of a contract.

Key Cases:

  1. Phillips v Brooks Ltd [1919]: In this case, the court held that where the seller intends to contract with the person in front of them, the contract is valid despite the buyer’s impersonation. The focus is on the seller’s intention to contract with the person present, regardless of the deception.
  2. King’s Norton Metal Co Ltd v Edridge, Merrett & Co Ltd [1897]: This case illustrates a situation where the seller was misled into believing they were dealing with a reputable company due to a deceptive order form. The court found that the contract was voidable due to the mistake as to the buyer’s identity.

Legal Principles:

  • The distinction between face-to-face and non-face-to-face transactions is crucial. In face-to-face transactions, the presumption is that the contract is with the person present, unless there’s evidence of a different intention.
  • In non-face-to-face transactions, particularly those involving written communication, the risk of fraud increases, and the courts are more willing to find a mistake as to identity that can render the contract void.

Mistake as to Terms

A mistake as to terms occurs when one party is mistaken about what the contract entails. This misunderstanding must relate to a fundamental term of the contract.

Key Cases:

  1. Hartog v Colin & Shields [1939]: This case involved a mistake regarding the price per unit of hare skins. The court held that the contract was void due to the buyer’s knowledge of the seller’s mistake, emphasizing that a contract requires a meeting of minds on all fundamental terms.
  2. Smith v Hughes [1871]: This case demonstrates that a mistake as to the quality of the goods being purchased does not necessarily void a contract. The buyer’s belief about the quality of oats being old rather than new was not considered a fundamental mistake that would invalidate the contract.

Legal Principles:

  • The mistake must be about a fundamental term of the contract. Not all mistakes will lead to the contract being voidable.
  • There must be evidence that the other party was aware of the mistake for it to affect the contract’s validity.


Understanding unilateral mistakes in contract law requires a careful analysis of the circumstances surrounding the contract’s formation. Mistakes as to identity and terms are treated differently, with specific cases illustrating how the courts approach these issues. It’s important to note that the details of each case can significantly influence the outcome, and these principles are subject to interpretation by the courts.

For those studying contract law, it’s crucial to delve into these cases and principles to understand how unilateral mistakes can impact the enforceability of contracts. Consulting with legal texts and resources can provide deeper insights into these complex issues.

Remember: This overview is intended for educational purposes and does not constitute legal advice. For specific cases or legal questions, consulting a legal professional is recommended.

For further reading on contract law principles, the UK Legislation website and legal textbooks on contract law are valuable resources.

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