PER - The parol evidence rule generally prevents parties from introducing extrinsic evidence of a prior or contemporaneous agreement that contradicts or varies the terms of a written contract. To apply: 1. See if the contract was validly formed, adhering to Statute of Fraud. 2. See if contract was intended to be the final expression of some terms or or all of the terms within the contract. Partially vs full integrated contract. 3. Fully integrated contracts: PER generally bars extrinsic evidence from supplementing or contradicting the contract. This means the offeror and offeree has intended everything terms to be finalized in the contract, and too bad-so sad if they wanted to add or change to the contract. 4. Partial integratedcontracts: PER may allow extrinsic evidence in that helps supplement the contract, but cannot contradict the contract. This means the offeror and offeree wanted to have a valid contract to get started, they were happy with the terms they had within that contract, but there is a possibility that a consistent promise was made, was relied upon, but did not completey make it onto the contract and may still be brought in as long as it doesnt contradict what is already on the contract.