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.
Waiver by one of the parties to the contract is conclusive as to third parties, at least as to those who claim under the party who has waived his right to take advantage of breach.1 A contract by a stepson to assist his stepfather,2 or by a child to live with a man and his wife as their child,3 or a contract of subscription to a college,4 are each sufficiently performed where the promisee accepts such performance as satisfactory to himself. Third persons can not thereafter object that such contract was not performed. If a third person claims under a contract between two other parties, he may take advantage of waiver by one of such parties of provisions of such contract.5 If A, who is a mortgagee under a construction mortgage, agrees to make certain payments to a subcontractor when the principal contractor has completed the work, and A subsequently agrees with the principal contractor that certain items may be omitted, A can not resist making such payment to the subcontractor on the ground that the principal contractor did not complete the work in accordance with the terms of the original contract.6
17 McConihe v. New York & Erie Ry., 20 N. Y. 405, 75 Am. Dec. 420.
18 Chamberlin v. Booth, 135 Ga. 719, 35 L. R. A. (N.S.) 1223, 70 S. E. 569.
1 Rogers v. Galloway Female College, 64 Ark. 627, 39 L. R. A. 636, 44 S. W. 454; Mills v. McCaustland, 105 la. 187, 74 N. W. 930; Burns v. Smith, 21 Mont. 251, 69 Am. St. Rep. 653, 53 Pac. 742; Burdine v. Burdine, 98 Va. 515, 81 Am St. Rep. 741, 36 S. E. 992.
2 Mills v. McCaustland, 105 la. 187, 74 N. W. 930.
3 As consideration for a contract to make a will. Burns v. Smith, 21 Mont. 251, 69 Am. St. Rep. 653, 53 Pac. 742.
For a similar case, see Burdine v. Burdine, 98 Va. 515, 81 Am. St. Rep. 741, 36 S. E. 992.
4 Rogers v. Galloway Female College, 64 Ark. 627, 39 L. R. A. 636, 44 S. W. 454.
5 Swartzman v. Babcock, 218 Mass. 334, 105 N. E. 1022.