According to the evidence rule, when parties have executed a written agreement which is complete on its face, oral agreements made before or at the same time as the written agreement that vary, alter, or contradict the written agreement are invalid.

Parol evidence rule.

Explanation: The word 'parol' comes from the French word 'parler' meaning argument or speech. The rule, in particular. stands in the protection of any of the parties involved, from the evidential factors like the 'bad memory'. Parties involved in legal matters take advantage of this rule in order to restrict the other party from bringing up pieces of evidence or saying anything that they had not talked about earlier in the agreement.