Parol Evidence Rule
A common law doctrine that prevents parties from introducing prior or contemporaneous oral statements to contradict the terms of a fully integrated written contract.
What Is the Parol Evidence Rule?
The parol evidence rule limits the use of extrinsic evidence — oral statements, prior negotiations, or earlier writings — to contradict, vary, or add to the terms of a written contract that the parties intended as a complete and final expression of their agreement. The rule promotes contractual certainty by giving the written document priority over informal discussions that led up to it.
When the Rule Applies
- The contract must be integrated (intended as the final agreement) - Full integration bars all extrinsic evidence on covered subjects - Partial integration bars contradictory evidence but allows consistent additional terms - The rule applies to prior and contemporaneous statements, not later modifications
Common Exceptions
Courts admit parol evidence to prove fraud, duress, mistake, illegality, lack of consideration, or to clarify ambiguous terms. Evidence of a separate collateral agreement may also be admissible if it does not contradict the writing. Many contracts include an integration clause (merger clause) explicitly stating that the writing is the complete agreement, which strengthens the application of the rule. Courts in jurisdictions following the modern approach may consider extrinsic evidence to determine whether the contract is ambiguous in the first place.