Parol Evidence Rule

This appears to be a principle of contracts that attempts to resolve disputes about what obligations in a contract are enforceable. In particular, the Parol Evidence Rule seeks to limit terms and conditions that were not included in the final executed contract. If a final agreement is signed, the only terms that are enforceable under that agreement are those that appear in the writing. Previous oral negotiations or proposed elements of a final writing are not enforceable in these cases.

Justice Andrews in 1928 describes it as, "a rule of law which defines the limits of the contract to be construed." Even if the parties concede that an oral agreement was made, that oral agreement is still not enforceable if there was a subsequent written agreement that did not include the orally-agreed-upon condition.

Now, the parol evidence rule does not apply if it can be shown that the oral agreement was sufficiently distinct and unrelated to the subsequent written contract. Thus, if I agree orally to sell you my car, and 5 minutes later sign a contract to mow your lawn, neither you nor I can void the oral agreement to sell the car based on the parol evidence rule. The two contracts are unrelated. This is an obvious example, but it would not take much imagination to conjure a situation in which the line between related and unrelated is more blurry.

Let's say that you and I orally agree that I will supply you with lawn ornaments at a reduced price, and five minutes later we sign an agreement that I will mow, fertilize, and maintain the general upkeep of your lawn (no mention of the lawn ornaments). Is the oral agreement to supply lawn ornaments relevant enough to the written contract that it should have been in the contract (such that its absence implies a lack of final agreement), or is it an entirely different matter that stands distinct and unaffected by the written agreement? Drawing the line in this case would depend on how much we view the supply of lawn ornaments to be a part of "the general upkeep" of one's lawn.