As a general rule, extrinsic evidence, whether written or oral, is not admissible to prove either the intent of the parties to a contract or the meaning of contractual terms when the parties have executed an unambiguous, fully-integrated (i.e., final and all-inclusive) written agreement. The trial court may consider various types of extrinsic evidence, however, in determining whether a particular agreement is fully integrated or ambiguous, and even in choosing among rival interpretations of an agreement where ambiguity is not present. If the trial court determines that an agreement is not fully integrated, then the trier of fact may consider extrinsic proof that supplements it. If the trial court determines that an agreement is ambiguous, then the trier of fact may consider extrinsic proof of the parties' contractual intent.
This Article identifies and examines the rules of construction used by Texas courts in determining contractual intent under Texas law, as well as the circumstances under which extrinsic evidence may be admitted either to supplement existing contractual terms or to demonstrate contractual intent. Practitioners responsible for drafting contracts and their colleagues who handle contract litigation should benefit from this examination. Part II of this Article discusses the fundamental common-law tenets of construction and interpretation applicable to all contract disputes. Part III addresses the concepts of ambiguity and integration, the common-law parol evidence rule, the parol evidence provisions of the Uniform Commercial Code, and the circumstances under which extrinsic evidence may be considered by Texas courts and juries.
49 Baylor L. Rev. 657 (1997).
Rowley, Keith A., "On Parol: The Construction and Interpretation of Written Agreements and the Role of Extrinsic Evidence in Contract Litigation" (1997). Scholarly Works. 550.