Restatement Second of Contracts § 214
Evidence of Prior or Contemporaneous Agreements and Negotiations
Agreements and negotiations prior to or contemporaneous with the adoption of a writing are admissible in evidence to establish
- that the writing is or is not an integrated agreement;
- that the integrated agreement, if any, is completely or partially integrated;
- the meaning of the writing, whether or not integrated;
- illegality, fraud, duress, mistake, lack of consideration, or other invalidating cause;
- ground for granting or denying rescission, reformation, specific performance, or other remedy.