Contract Law: the Issue of Mutual Mistake of Fact

Categories: Mistakes


Mutual Mistake of fact occurs when both parties to a contract operate under a shared assumption of fact at the time the contract is formed and signed. This mistake must be of such significance that it fundamentally alters the contractual obligations to the extent that it transforms the agreement into an entirely different contract. However, if one party had knowledge or awareness of a substantial probability of the mistake when signing the contract, that party assumes the risk associated with the mistake and cannot invoke the mutual mistake defense.

It is crucial to note that not all cases of Mutual Mistake are robust enough to render a contract void.

An Analysis of Mutual Mistake in Contract Law

In the context of contract law, Mutual Mistake of fact is a defense that can be raised by a party seeking to avoid their contractual obligations. This defense asserts that both parties to the contract operated under a mistaken assumption when entering into the agreement, rendering the contract void.

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To qualify as a mutual mistake, the mistaken assumption must be a fact that both parties believed to be true at the time the contract was executed.

Let's consider a hypothetical case involving Josh Hartly, who expressed his intention to purchase a new car from his local auto dealer. During negotiations, Josh specified his preference for a car equipped with a 3.

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2 liter V6 engine rather than one with a 3.9 liter engine due to concerns about fuel economy. Subsequently, Josh signed a contract agreeing to purchase the car with a 3.2 liter V6 engine. Unbeknownst to both Josh and the salesperson, the manufacturer had already ceased production of both the 3.2 liter and 3.9 liter engines, opting instead for a newly designed 3.5 liter engine for their cars.

This scenario presents a classic example of a mutual mistake of fact. Both parties operated under the assumption that Josh would receive a car with a 3.2 liter V6 engine, a fact that was integral to the contract. However, due to the manufacturer's decision to discontinue these engine models, this crucial fact is no longer accurate. Consequently, the salesperson can no longer fulfill the contract as originally intended, making the contract void.

The concept of Mutual Mistake of fact serves as a fundamental principle within contract law, ensuring that contractual agreements remain fair and just. In cases where both parties were unaware of a material fact that significantly impacts the contract, it is only equitable to void the agreement and release both parties from their obligations (LaMance, 2011).

It is important to emphasize that not all errors or mistakes in contracts qualify as mutual mistakes. To warrant the mutual mistake defense, the error must be of such a magnitude that it fundamentally transforms the nature of the contract, rendering it an entirely different agreement from what was originally intended. Minor or inconsequential mistakes are unlikely to meet this threshold and would not justify voiding the contract.

The Ethical Perspective

In evaluating the situation involving Josh Hartly and the auto salesperson, it is crucial to consider the ethical dimension. While one might argue that the salesperson should have been aware of the manufacturer's decision to discontinue certain engine models, thus making it a unilateral mistake of fact, it is equally important to recognize that ethical responsibility is not solely the purview of one party.

Buying a new car is a significant transaction, and potential buyers bear a responsibility to conduct their due diligence and research. In this case, Josh Hartly could have taken the initiative to inquire about any imminent changes to the car's specifications or engine options. Ethical responsibility extends to both parties in a contract, and it is essential for all parties to act in good faith and with transparency.

While the salesperson's lack of awareness regarding the manufacturer's decision may raise ethical questions, it is equally important to consider the role of personal responsibility. In contract law, parties are expected to enter into agreements with a reasonable level of awareness and knowledge. Therefore, mutual mistakes that arise from a lack of diligence or inquiry on the part of one party may not always warrant the defense of mutual mistake.

The Role of the Uniform Commercial Code (UCC)

The Uniform Commercial Code (UCC) plays a significant role in governing contract disputes related to the sale of goods. The UCC is a comprehensive model statute that has been adopted in its entirety by every state in the United States. While the UCC is primarily applied to resolve contract disputes involving the sale of goods, it is essential to note that it exclusively pertains to merchants.

Merchants, as defined by the UCC, are individuals or entities with specialized knowledge in a particular commercial field. Therefore, contracts for the sale of goods between private, non-merchant parties do not fall under the purview of UCC requirements (Rivera, 2013).

It is important to emphasize that the UCC is not a one-size-fits-all framework but rather a set of guidelines designed to address the unique complexities of commercial transactions. It provides a framework for resolving disputes related to the sale of goods, including issues of contract formation, performance, and remedies.

Assessing Winners and Losers

In the context of mutual mistake defenses, it is challenging to identify clear winners and losers. The outcome of invoking a mutual mistake defense typically results in the contract being deemed void, thereby releasing both parties from their respective obligations.

From one perspective, the party raising the mutual mistake defense may be seen as a winner, as they successfully avoid fulfilling a contract that has been fundamentally altered due to the mistake. However, it is essential to recognize that they are still without the goods or services they initially sought to obtain through the contract. In the case of Josh Hartly, while he may no longer be obligated to purchase a car with a 3.2 liter V6 engine, he is left without the specific vehicle he desired.

Conversely, the party that would have performed under the original terms of the contract is often viewed as a loser in this scenario. In the case of the auto salesperson, they have not only lost a potential sale but also expended time and resources in negotiating and drafting the contract. As a result, both parties are left in a situation where the original transaction cannot be completed.


In conclusion, Mutual Mistake of fact represents a vital aspect of contract law, ensuring fairness and equity in contractual agreements. When both parties to a contract operate under a shared mistaken assumption that significantly alters the nature of the agreement, it is justifiable to void the contract. However, it is important to recognize that not all errors in contracts qualify as mutual mistakes, and the threshold for invoking this defense is high.

Ethical responsibility and due diligence play a crucial role in contract formation, and all parties are expected to act in good faith. Additionally, the Uniform Commercial Code (UCC) provides a framework for resolving contract disputes related to the sale of goods, primarily for merchants with specialized knowledge in commercial fields.

In assessing winners and losers in cases involving mutual mistake defenses, it becomes evident that both parties may experience losses. While one party may avoid fulfilling an altered contract, they may still be without the goods or services they originally sought. Simultaneously, the other party may lose a potential sale and incur expenses related to the negotiation and drafting of the contract. In the realm of contract law, mutual mistakes underscore the importance of clear communication, ethical conduct, and responsible due diligence in contractual relationships.

Updated: Jan 08, 2024
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Contract Law: the Issue of Mutual Mistake of Fact. (2016, May 10). Retrieved from

Contract Law: the Issue of Mutual Mistake of Fact essay
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