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.
In some states it is provided by statute that a written contract can be modified only by a contract in writing, or by an executed oral agreement. Under such statute, an executory oral agreement, even if otherwise valid, cannot operate to modify a prior written contract.1 Under such statutes there is a conflict of authority as to what constitutes an executed contract. An agreement between an insurance company and a policy holder after a loss fixing the amount of the liability of the company, is not a "modification" of the policy within the meaning of the statute, forbidding executory oral modifications of written contracts.2 On the other hand, a written contract for sinking a well provided that if four and a half inch piping were used the price should be fifteen hundred dollars; but if three inch piping had to be used the price should be nine hundred fifty dollars. Subsequently after four and a half inch piping could be and was used for the greater part of the distance, the parties agreed orally that three and a half inch piping should be used for the rest of the distance and that the price should be fifteen hundred dollars. Pipe of this size was put in, and more than nine hundred fifty dollars was paid. It was held that the contractor could not recover the balance as the contract was still executory.3
7 Copeland v. Hewett, 96 Me. 525; 53 Atl. 36.
8 Gibbs v. School District, 195 Pa. St. 396; 46 Atl. 91.
9 Consaul v. Sheldon, 35 Neb. 247; 52 N. W. 1104; De Mattos v. Jordan, 15 Wash. 378; 46 Pac. 402.
10 Northern Light Lodge v. Kennedy, 7 N. D. 146; 73 N. W. 524. (Criticising the opinions in the cases in the previous note as obiter.)
12 Continental Ins. Co. v. Pearce, 39 Kan. 396; 7 Am. St. Pep. 537; 18 Pac. 291; Westchester, etc., Ins. Co. v. Earle, 33 Mich. 143; Pechner v. Ins. Co., 65 N. Y. 195; American Central Ins. Co. v. McCrea, 8 Lea (Tenn.) 513; 41 Am. Rep. 647. Provision against other insurance.
Fireman's Fund Ins. Co. v. Norwood, 69 Fed. 71; 16 C. C. A. 136; Morrison v. Ins. Co., 69 Tex. 353; 5 Am. St. Rep. 63; 6 S. W. 605.
12 Carpenter v. Ins. Co., 16 Pet. (U. S.) 495.
1 Thompson v. Garner, 104 Car. 168; 45 Am. St. Rep. 81; 37 Pac. 900; Benson v. Shotwell, 103 Cal. 163; 37 Pac. 147; Erenberg v. Peters, 66 Cal. 114; 4 Pac. 1091; Mettel v. Gales, 12 S. D. 632; 82 N. W. 181. In Mettel v. Gales, 12 S. D. 632; 82 N. W. 181, this statutory rule is spoken of as Common Law doctrine, apparently on the theory that it is the same thing as the parol evidence rule.