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 order that the promisee may be held to waive a breach of the contract, he must know of the fact which constitutes such breach.1 So the act of an insured in waiving one ground of forfeiture, does not affect the waiver of another ground of which the insured was ignorant.2 So the acceptance of the performance of a contract to construct a drain, made as the result of fraud or mistake, does not amount to a final waiver of breach.3 So, in order that acceptance of defective performance of a building contract may operate as a waiver it must be shown that the owner knew of the defects in performance.4 The fact that the departure from the specifications was plain does not dispense with knowledge thereof by the owner.5 If it is claimed that if one who has a right under contract to have his portrait inserted in a certain history, has accepted in place thereof its insertion in a so-called " portrait gallery " from which historical matter is omitted, it must be shown that he had full knowledge of his rights under the contract and that his portrait was omitted from the sort of work in which he had a right to have it inserted.6 However if the want of knowledge is the fault of the party who is alleged to have waived a breach committed by the adversary party, his conduct may amount to a waiver of the breach, even if its existence is unknown to him.7 Thus, if proof of printing is submitted to the party for whom the work is done, and he approves it, overlooking an error, he cannot object to such error in the finished work as a breach.8
N. D. 88; 73 N. W. 70; Laycock v. Moon, 97 Wis. 59; 72 N. W. 372; Tickler v. Mfg. Co., 95 Wis. 352; 70 N. W. 292.
2 Pratt v. Mfg. Co., 115 Wis. 648; 92 N. W. 368.
3 Forbes v. Appleyard, 181 Mass. 354; 63 N. E. 894.
4 Avery v. Bowden, 5 E. & B. 714.
5 Gray v. New Paynesville, 89 Minn. 258; 94 N. W. 721.
6 Mahaska County State Bank v. Crist, 87 la. 415; 54 N. W. 450.
1 Loudenback Fertilizer Co. v. Phosphate Co., 121 Fed. 298; Yor-ston v. Brown, 178 Mass. 103; 59 N. E. 654; Stevenson v. Log-Tmv-ing Co., 103 Mich. 412; 61 N. W. 536.
2 Planters' Mutual Ins. Co. v. Loyd, 67 Ark. 584; 77 Am. St. Rep. 136; 56 S. W. 44.
3 Van Akin v. Dunn. 117 Midi.