Pym v. Campbell
Queen's Bench
6 Ellis & Blackburn 370 (1856)
Campbell (defendant) signed a written agreement with John Pym (plaintiff) to purchase a share of benefits from Pym's invention, but at trial Campbell was permitted to introduce evidence that the parties' agreement was actually conditioned on two engineers approving the invention, one of whom disapproved, leading Campbell to refuse payment. The trial judge ruled for Campbell based on this evidence, and Pym obtained a rule nisi seeking a new trial on the ground that this evidence should have been excluded under the parol evidence rule.
Whether evidence showing that a written agreement was conditioned on the happening of an event is admissible, despite the general rule barring parol evidence that varies the terms of a written agreement.