The purpose of the parol evidence rule is to allow oral evidence to prove agreements, and it is an essential principle in contract law. In essence, the rule establishes that if there is a written contract between two parties, then the parties cannot introduce any oral or written evidence that contradicts or modifies the terms of the written contract. However, there are some exceptions to this rule.

One of the main purposes of the parol evidence rule is to ensure that the parties to a contract are bound only by the terms set out in the written agreement. This helps to prevent disputes and misunderstandings that might arise if parties could introduce evidence of prior negotiations or agreements. Additionally, the rule ensures that parties can rely on the written contract as the final and complete expression of their agreement.

The parol evidence rule applies to almost all types of contracts, including employment agreements, lease agreements, and sales contracts. However, there are some exceptions to the rule. For example, evidence may be admissible if it is intended to explain an ambiguity in the contract. Similarly, evidence may be admissible if it is necessary to prove that the contract was void or voidable, or to establish fraud, duress, or mistake.

Another important exception to the parol evidence rule is the rule of evidence of contemporaneous negotiations. This rule allows evidence of prior oral or written negotiations between the parties to be admitted in order to establish the meaning of terms in the contract. In other words, if there is an ambiguity in the written contract, then evidence of prior negotiations or agreements may be used to clarify the meaning of the disputed term.

Overall, the parol evidence rule is an important principle in contract law that helps to ensure that parties are bound only by the terms of the written agreement they have signed. While there are some exceptions to the rule, courts generally apply it strictly in order to prevent disputes and misunderstandings. As a professional, it is important to understand the purpose of this rule and to use appropriate language and terminology when writing about it.