Hartog v Colin and Shields

March 04, 2024
Micheal James

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Hartog v Colin and Shields (1939) occupies a critical position in English contract law, addressing the thorny issue of whether a contract remains valid when one party enters into it under a unilateral mistake regarding the price of goods. The case revolved around a misunderstanding during negotiations for hare skin purchases, sparking a legal debate about the very essence of contract formation: mutual understanding and genuine consent.


Mr. Hartog, a Belgian furrier, entered into oral negotiations with Colin and Shields, hide merchants, for the purchase of 30,000 Argentine hare skins. The initial understanding was a price of 4d per skin, a typical market rate. However, upon committing the agreement to writing, Colin and Shields mistakenly wrote the price as 7d per skin, significantly higher than agreed upon. Hartog, unaware of the discrepancy, readily accepted the written offer upon receiving it.

Procedural History

Upon realizing the miscalculation, Colin and Shields refused to honor the sale at the 7d price. Hartog, claiming a binding contract existed, sued them for breach of contract. The initial trial court sided with Colin and Shields, finding the contract void due to Hartog’s mistaken understanding of the price. Not satisfied, Hartog appealed the decision, arguing that his immediate acceptance formed a valid contract despite the misunderstanding.


Hartog argued that his acceptance of the written offer, regardless of the erroneous price, created a binding contract. He highlighted that his intention to accept at 4d per skin was irrelevant due to the objective manifestation of acceptance through his actions. He further emphasized the detrimental reliance on the contract he had placed by preparing for the shipment.

Colin and Shields, on the other hand, countered by asserting the absence of genuine consent, a fundamental element of contract formation. They argued that Hartog’s acceptance stemmed from a misconception of the terms and did not reflect his true intentions. They emphasized the importance of consensus ad idem – a meeting of minds – and argued that a valid contract cannot exist when one party operates under a material mistake.

Legal Analysis

The Court of Appeal upheld the initial decision, siding with Colin and Shields. Judge Singleton, delivering the judgment, acknowledged the general principle of acceptance forming a binding contract upon manifestation. However, he highlighted the exception in cases of unilateral mistake, particularly where it concerned a material term like price.

The court concluded that Hartog, aware of the usual price for hare skins, must have recognized the significant discrepancy in the written offer. They held that his acceptance in such circumstances did not reflect genuine consent but rather a “snapping up” of an advantageous offer he knew to be based on a mistake. This lack of consensus ad idem, they argued, rendered the contract void.

Impact and Implications

Hartog v Colin and Shields established a crucial precedent in English contract law regarding unilateral mistake. The case emphasized the importance of mutual understanding and clarified that mere acceptance does not suffice if it stems from a misunderstanding of the terms, especially when concerning material aspects like price. This established a protective measure against unfair outcomes and promoted the need for open and accurate communication during contract formation.

However, the decision also sparked some debate. Critics argued that it could potentially allow parties to escape unfavorable contracts by claiming a unilateral mistake, creating potential uncertainty. Nonetheless, the case remains a foundational reference point in discussions about mistake in contract formation, influencing its application in subsequent legal proceedings.


Hartog v Colin and Shields stands as a significant milestone in English contract law, offering a nuanced understanding of how unilateral mistake can impede the formation of a valid contract. The case highlighted the importance of genuine consent and mutual understanding, establishing a framework for ensuring fairness and accuracy in contractual engagements. While its implications continue to be debated, the case undeniably left a lasting mark on the legal landscape, reminding parties of the need for clear communication and careful consideration to avoid potential pitfalls in contract formation.

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