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.
To constitute an alteration the change in the language of the written instrument must have been made intentionally. If not intentional, it is not an alteration.1 Placing internal revenue stamps on the face of a shipping receipt is not the erasure or alteration of any part of such receipt or contract covered thereby.2 So if a waiver of demand and notice and a guaranty of payment is affixed with a stamp and by mistake is placed above the signature of an indorser who did not waive or guarantee, instead of over the signature of the one who did, this does not discharge such indorser.3 So if by mistake an indorsement is cancelled on the wrong note,4 or one who means to sign as surety signs in the place appropriate for a witness,5 the contract is not thereby discharged. In the foregoing cases thereby was no intent to make the alteration in question at all. The mistake was analogous to a mistake in execution.6 The principle has been extended to alterations which the party making them intended to make, but such intention was caused by mistake of fact as to some collateral material fact.7 So if a holder believing that an instrument is to be paid,8 or has been paid,9 cancels it, such cancellation is not such alteration as discharges it. So an alteration made through a mistake of law while attempting to accomplish some lawful purpose, has been held not to discharge the contract. An example of this is found where one wishes to transfer a negotiable instrument and attempts to do so by substituting the name of the indorsee for that of the original payee.10 If a guarantor by inadvertence signs his name in such a way as to indicate prima facie that he is an original promisor, the contract is not discharged thereby.11
»Lee v. Butler, 167 Mass. 426; 57 Am. St. Rep. 466; 46 N. E. 52.
10 McMillan v. Hefferlin, 18 Mont. 385; 45 Pae. 548.
11 Pelton v. Lumber Co., 113 Cal. 21; 45 Pac. 12.
12 Murray v. Graham. 20 la. 520; Letcher v. Bates, 6 J. J. Mar. (Ky.) 524; 22 Am. Dec. 02; Evans v. Foreman, 60 Mo. 440; Hunt v. Gray, 35 N. J. L. 227: 10 Am. Rep.
232; Smith v. Smith, 27 S. C. 166; 13 Am. St. Rep. 633; 3 S. E. 78.
1 Sloman v. Express Co., - Mich. -; 05 N. W. 999; Rhoads v. Frederick. 8 Watts (Pa.) 448.
2 Sloman v. Express Co., - Mich. -; 05 N. W. 000.
3 Gordon v. Bank, 144 U. S. 07.
4 Brett v. Marsten, 45 Me. 401.
5 Fisher v. King, 153 Pa. St. 3; 25 Atl. 1029.