Pym v Campbell (1856) 6 E & B 370
The parol evidence rule and the construction of the terms of a written contract.
Facts
Pym and Campbell signed a written agreement wherein Campbell agreed to purchase three-eighths of the profits to accrue from Pym’s new invention. The invention did not receive the requisite approval from one of Campbell’s engineers and, accordingly, Campbell refused to pay Pym the purchase price. Pym sued for breach of contract. However, Campbell claimed that the agreement was conditional upon the approval of the invention, presenting oral evidence of party negotiations to that effect.
Issues
The question arose as to whether the oral evidence, extrinsic to the terms of the written contract, was admissible before the Court and able to alter the construction of said written contract and/or show that it was unenforceable.
Decision/Outcome
The Court held that, as a general rule of law, the terms contained within a signed written contract are conclusive and cannot be varied by parol evidence. Thus, parol evidence cannot introduce an addition to or variation from the terms of a written contract between the Parties. However, in this case, the Court held that the general parol evidence rule is not applicable as the question did not concern the construction of the terms of a contract but rather whether there was any agreement at all. Thus, parol evidence that sought to show that the agreement was never entered into was admissible. On the facts, the Court held that there was overwhelming evidence from the oral negotiations between the Parties that, prior to signing the written document, the Parties came to a mutual understanding the prospective purchase was not intended to be an agreement until the invention was approved by the engineers. As there was no approval, there was no agreement and Campbell was not obliged to pay Pym.
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Updated 20 March 2026
This article accurately describes the decision in Pym v Campbell (1856) 6 E & B 370, a foundational English contract law case on the parol evidence rule. The legal principles described remain good law. The parol evidence rule, and the recognised exception permitting oral evidence to show that a written document was not intended to take effect as a binding contract at all (as distinct from varying or adding to its terms), continues to be applied by English courts. The rule and this exception are well established in modern contract law and are routinely discussed in leading contract law texts and judgments. There have been no statutory or judicial developments that would undermine or materially alter the principles set out in this case. Readers should note, however, that the parol evidence rule has been subject to ongoing academic and judicial commentary regarding its scope and limitations, and in practice its strictness is often tempered by doctrines such as rectification, collateral contracts, and implied terms. The article provides a sound introductory summary suitable for students.
