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.
Whether the alteration of one contract affects another contract or instrument in some way connected with the former instrument is a question sometimes presented for consideration. A material alteration in one of two instruments secured by a mortgage does not discharge the other.1 A material alteration of some of a series of notes given under a conditional contract of sale does not avoid the contract of sale or the rest of the notes.2 An alteration which avoids a mortgage does not avoid the note to secure which it was given.3 Whether the alteration of a note discharges the mortgage given to secure the note depends on the nature of the alteration and the purpose with which it was made. An immaterial alteration would, of course, have no effect on either note or mortgage. Such an alteration does not, therefore, discharge the mortgage. A material alteration, if innocent, discharges the written contract, but leaves the obligor thereon liable for the original consideration received by him, and the mortgage remains as a valid security for such debt.4 On the other hand, a material fraudulent alteration discharges the original liability and therefore discharges the mortgage.5
Frye. 10 Mo. 348; Walton Plow Co. v. Campbell, 35 Neb. 173; 16 L. R. A. 468; 62 N. W. 1078; Marten-dale v. Follett, 1 N. H. 95; Bank of Decorah v. Laughlin, 4 N. D. 391; 61 N. W. 473; Bigelow v. Stilphen, 35 Vt. 521; Newell v. Mayberry, 3 Leigh (Va.) 250; 23 Am. Dec. 261. 2 Glover v. Green, 96 Ga. 126; 22 S. E. 664. See for similar facts, Singleton v. MeQuerry, 85 Ky. 41; 2 S. W. 652.
1 Parke, etc., Co. v. Lumber Co. 110 Cal. 658; 43 Pac. 202.
2 Edward Thompson Co. v. Baldwin, 62 Neb. 530; 87 N. W. 307.
3 Kime v. Jesse, 52 Neb. 606; 72 N. W. 1050.
4 Elliott v. Blair. 47 111. 342: Clough v. Seay, 49 la. Ill; Baskin v. Wayne. 62 Mo. App. 515; Gil-lett v. Powell. Speers Eq. (S. C.) 142; Plyler v. Elliott, 19 S. C. 257; Smith v. Smith. 27 S. C. 166; 13 Am. St. Rep. 633; 3 S. E. 78.