Legal Case Summary
Cooper v Phibbs (1867) LR 2 HL 149
Contract – Void – Mistake- Mistake as to Title – Res Sua – Beneficial Ownership – Lease – Equity – Voidable
Facts
The complainant, Mr Cooper, was the nephew of the owner of the salmon fishery near Ballysadare, Ireland. He leased this salmon fishery from his Uncle. When his uncle died and the lease came up for the time of renewal, the complainant renewed the lease for the salmon fishery with his Aunt. However, it was later found out that in the Uncle’s will, Mr Cooper as his nephew, had been given life tenancy of the salmon fishery. This meant that there was no need for the lease that existed between him and the Aunt and the dispute arose when the next rental payment was due.
Issue
The issue in this case was whether Mr Cooper was the owner of the salmon fishery and whether the lease would be void.
Decision / Outcome
It was held that the contract and lease that existed between the complainant and the defendant was voidable, rather than void. This was due to the claim being in equity, as Mr Cooper had beneficial ownership of the salmon fishery and not legal ownership. This case concerned ‘res sua’ and it was a mistake as to the title of the property; Mr Cooper was already the beneficial owner of the salmon fishery and there could not be a lease. It was held that such an agreement would be set aside due to a common mistake by both parties as to ownership.
Updated 19 March 2026
This case summary accurately describes the decision in Cooper v Phibbs (1867) LR 2 HL 149, a foundational House of Lords authority on common mistake as to title (res sua) in equity. The core legal principle — that a contract entered into under a common mistake as to ownership may be voidable rather than void in equity — remains a recognised part of English and Irish private law.
Readers should be aware of one significant later development. The Court of Appeal in Great Peace Shipping Ltd v Tsavliris Salvage (International) Ltd [2002] EWCA Civ 1407 cast doubt on whether equity has a separate and broader jurisdiction to rescind contracts for common mistake beyond the narrow category where common law treats the contract as void. The Court of Appeal declined to follow Solle v Butcher [1950] 1 KB 671, which had relied on the equitable jurisdiction discussed in Cooper v Phibbs. The precise relationship between the common law and equitable approaches to common mistake therefore remains unsettled, and Cooper v Phibbs itself was distinguished rather than overruled. Students should read this case alongside Great Peace Shipping and note the ongoing academic and judicial debate about the scope of equitable relief for common mistake.
