Parol Evidence Rule
Parol evidence may not be used to vary or contradict the express or implied terms of an unambiguous written agreement absent a showing of fraud, accident, or mutual mistake. Toler v. Sanders, 371 S.W.3d 477, 481 (Tex. App.-Houston [1st Dist.] 2012, no pet.); Hudson Buick, Pontiac, GMC Truck Co. v. Gooch, 7 S.W.3d 191, 198 (Tex. App.-Tyler 1999, pet. denied). Evidence admitted in violation of the parol evidence rule is incompetent and without any probative force. Johnson v. Driver, 198 S.W.3d 359, 364 (Tex. App.-Tyler 2006, no pet.).
SOURCE: HOUSTON COURT OF APPEALS – 14-11-00895-CV – 4/30/2013