For more than 80 years, the rule in California was that a party to a written contract may not introduce oral or other evidence in court that contradicts a specific promise in that contract. 

Some exceptions are recognized. But if any party to a contract could challenge it simply by claiming that it doesn’t represent the real contract, then the integrity of contracts is undermined. This month, the California Supreme Court overturned its own 1935 decision and, by doing so, opens the courthouse doors to plaintiffs to challenge written contracts based on oral or other promises allegedly made by the other contractual party. 

See CBA’s Legal Notes for an analysis of RiverIsland Cold Storage Inc. v. Frenso-Madera Production Credit Assn.