The evidence rule attempts to protect sales or lease contracts that the parties intended to be the final expression of their agreement.

The evidence rule, also known as the Parol Evidence Rule, is a principle in contract law that prevents parties from introducing evidence of prior or contemporaneous negotiations and agreements that contradict, modify, or vary the contractual terms of a written contract when the written contract is intended to be a complete and final expression of the parties’ agreement.

Here are the steps to understand this rule:

1. Identify the Written Contract: The rule applies only to written contracts that are intended to be the final agreement between the parties.

2. Determine if the Contract is a Final Expression: The rule only applies if the written contract is intended to be the final expression of the parties' agreement. This means that the contract includes all terms and conditions agreed upon and there is no need for further negotiation or agreement.

3. Identify the Prior or Contemporaneous Agreement: The rule prevents parties from introducing evidence of prior or contemporaneous agreements. This means that any agreement or negotiation that took place before or at the same time as the written contract cannot be used to contradict, modify, or vary the terms of the written contract.

4. Apply the Rule: If the written contract is intended to be the final expression of the parties' agreement, then any evidence of prior or contemporaneous agreements that contradict, modify, or vary the terms of the written contract is not admissible in court.

5. Exceptions: There are exceptions to the rule. For example, evidence of a prior or contemporaneous agreement may be admissible to clarify ambiguous terms in the contract, to prove a condition precedent, or to show that a contract was induced by fraud, duress, mistake, or illegality.