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 new promise creates a new liability supported by the original liability as a consideration, or whether the new promise merely waives the bar of the discharge and leaves the original liability in force is a question upon which there is a conflict of authority. Some authorities hold that the liabilty is on the new promise ;1 while other authorities treat the liability as being on the original claim.2 No good reason appears for refusing to hold that either theory of the nature of the debtor's liability may be entertained. The courts generally assume, however, that one or the other of these theories must be entertained to the exclusion of the alternative.