The rule applies to all written contracts, whether or not the status of fraud requires written form. The status of fraud relates to whether there has been a treaty; Parol`s rule of proof is that there was a written contract, does it express the understanding of the parties? However, the rule only applies to events that preceded the signing of the controversial contract. It has no influence on subsequent agreements that may modify the terms of an existing contract.  Many contracts contain clauses that require amendments to a written agreement, which must also be in writing, but are not always applicable. “No oral modification” clauses – or NOM clauses – are often included in commercial contracts as standard terms to limit changes or additions to future unintentional contracts. Oral contracts are often mistakenly referred to as oral treaties, but an oral contract is really any contract, since all contracts are written in language. The rule of evidence parol Under this rule, when there is a written contract, extrinsic evidence (speech) generally cannot change the explicit conditions set out in this document. (parol means oral; it refers to Parliament and parly – speaking) is a substantive rule of law that prevents the introduction of evidence intended to show that the parties have agreed on something other than what they have finally obtained and written. It applies to both prior written interviews and oral interviews that do not reach the final written agreement. 3 [the anti-oral amendment clause] does not, in principle, prevent them from subsequently concluding a new contract modifying the contract by oral agreement or conduct.