Parol Evidence Rule & Failure to Express True Intention of Parties

Under the parol evidence rule, when the terms of an agreement have been reduced into writing, it is considered as containing all the terms agreed upon, and there can be, between the parties and their successors-in-interest, no evidence of such terms other than the contents of the written agreement. However, a party may present evidence to modify, explain or add to the terms of the written agreement if he puts in issue in his pleading, the failure of the written agreement to express the true intent of the parties thereto. [G.R. No. 121506. October 30, 1996]