This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
A written contract frequently contains an express provision to the effect that all the terms of the contract between the parties are set forth in such writing. Such a term could not prevent a contract which on its face was incomplete from being treated as an incomplete contract. Whether such a provision could preclude the admission of oral evidence to show the remaining terms of such contract, or whether it would require the courts to treat the contract as so incomplete as to be unenforceable, is a question upon which there is little authority. If the contract is clearly complete upon its face, such a provision can, of course, add nothing to the legal effect of such contract. In doubtful cases, however, the insertion of such provision in a written contract strengthens the presumption that a written contract is complete and that it sets forth the entire contract between the parties.1 A contract of sale,2 or a contract for work and labor,3 which provides expressly that such written contract contains all the terms of the agreement between the parties, will be regarded as complete, at least if it does not show upon its face that the parties have agreed upon terms other than those which are set forth in the written contract. If a written contract provides expressly that no oral agreement has been entered into upon a certain subject, such provision is regarded as conclusive.4 A provision in a release of a claim for personal damages, to the effect that no agreement had been made for employment, was held to be conclusive.5
29 Arkansas. Merrill v. Sypert, 65 Ark. 51, 44 S. W. 462.
Georgia. Barrie v. Miller, 104 Ga. 312. 30 S. E. 840.
Kentucky. Chapman v. Clements (Ky.), 56 S. W. 646.
Michigan. Germain v. Lumber Co., 116 Mich. 245, 74 N. W. 644 [same case, 78 N. W. 1007].
Nebraska. State v. Cass County, 60 Neb. 566, 83 N. W. 733.
North Carolina. Doubleday v. Coal Co., 122 N. Car. 675, 30 S. E. 21.
Rhode Island. F. A. Thomas Machine Co. v. Voelker, 23 R. I. 441, 50 Atl. 838.
30 Greenfield v. Gilman, 140 N. Y. 168, 35 N. E. 435; Bruce v. Moon. 57 S. Car. 60, 35 S. E. 415.
31 Hoster's Committee v. Zollman, 122 Va. 41, 94 S. E. 164. See Sec. 87 et seq.
32 It was held inadmissible even where the payee had filled in such blank with the legal rate. Haas v. Commerce Trust Co., 104 Ala. 672, 69 So. 894.