Parol Evidence Rule

The parol evidence rule is a substantive common law rule in contract cases that prevents a party to a written contract from presenting extrinsic evidence that contradicts or adds to the written terms of the contract that appears to be whole. Parol = oral (Anglo-French / Anglo-Norman / Legal French). The supporting rationale is that since the contracting parties have reduced their agreement to a single and final writing, the extrinsic evidence of past agreements or terms should not be considered when interpreting that writing, as the parties had decided to ultimately leave them out of the contract. Basically, one may not use evidence made prior to the written contract to contradict the writing. A common misconception is that it is a rule of evidence (like the Federal Rules of Evidence), but that is not the case.