Parol

Parol is a legal term related to contracts, originating from the French word parole meaning spoken word. In contract law, it commonly appears in the phrase parol evidence rule, which governs whether evidence of terms not contained in a written agreement may be used to interpret, modify, or contradict that writing.

The parol evidence rule states that, when a contract is a fully integrated written instrument, extrinsic evidence of prior or contemporaneous oral agreements cannot be used to vary or contradict the terms of the writing. In other words, the written contract is treated as the complete and final expression of the parties’ agreement, and parole evidence cannot override its clear terms. If the contract is only partially integrated, extrinsic evidence may be admissible to supplement the writing but not to contradict its express terms.

There are several well-established exceptions to the rule. Extrinsic evidence may be admitted to prove the contract’s validity (fraud, duress, mistake, illegality), to establish a missing or ambiguous term, to show a separate collateral agreement, or to show course of dealing, usage of trade, or course of performance. Courts also allow parole evidence to interpret ambiguous language or to show that a merger clause is not controlling in certain circumstances.

Jurisdictional differences exist in how strictly the rule is applied and how exceptions are treated. In practice, parties often include integration or merger clauses to emphasize that the written document is meant to be final. Parol evidence remains a foundational concept in contract interpretation and dispute resolution.