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 cases of material alteration, where the written contract is discharged, the question then arises as to whether recovery can be had in quasi-contract on the original consideration for which the instrument was given. This depends on whether the alteration was made innocently or fraudulently. If it was made innocently, recovery can be had on the original consideration.1 Accordingly, in jurisdictions in which the alteration of a note, so as to make it conform to the actual agreement of the parties, is held to be material so as to avoid the instrument,2 the original debt can be recovered; 3 and a mortgage which is given to secure such note can be enforced for the original obligation.4