Parol evidence rule
Contract Law

The parol evidence rule that disallows parol evidence (that is, oral or verbal evidence) to be admitted to 'contradict, vary, add, to or subtract from the terms of a written contract' or a part of a contract that has been completely recorded in writing.

The rule is intended preserve the integrity of a written agreement and allow it to be interpreted using principles of contractual construction that promotes certainty, without interference from pre-contractual negotiations, draft contracts and other extrinsic matter.

There are a number of exceptions to the parol evidence rules under English law which include situations where:

1. the written document does not record the entire agreement between the parties, that is, where the agreement is partly verbal and partly written such as a oral term that is not recorded in the agreement, but was intended by the party to continue in force concurrently with the written terms.
2. a contract is alleged to exist which is collateral to the agreement. See collateral contract.
3. the formation of the contract is vitiated by mistake.
4. the document itself is not a contract.
5. the contract is conditional on some event taking place.
6. the evidence relates to the date the contract was entered into.
7. the contract has been varied.
8. the contract is tainted by fraud or some illegality.