This section is from the book "The Law Of Contracts", by Samuel Williston. Also available from Amazon: Treatise on the Law of Contracts.
A promise which is within the statute is often said to be collateral, if not within the statute it is called original. "The terms collateral or original promise did not occur in the statute, and have been introduced by courts of law to explain its objects and expound its true interpretation."81
In truth the use of these terms clearly antedates the Statute of Frauds. They were part of the terminology of the law governing the action of debt; an original promise being such a promise as would give rise to an action of debt because a quid pro quo had been received by the defendant; whereas a collateral promise though it might be a binding contract upon which assumpsit would lie because a detriment had been incurred by the plaintiff at the defendant's request, could not be the basis of debt.82 Though the illustrations of collateral the statute by the mere fact that some one other than the promisor has received the benefit of the consideration. Thus, a contract to pay for goods delivered to a third person,85 or to pay the board of a third person,86 or to pay for services rendered to a third person,87 or to repay money paid at the promisor's request to a third person,88 is original and enforceable though oral.
81 D'Wolf v. Rabaud, 1 Pet. 476,490, 7 L. Ed. 672. In Nelson v. Boynton, 3 Met. 396, 400, 37 Am. Dec. 148, Shaw, C. J., said: "The terms original and collateral promise, though not used in the statute, are convenient enough to distinguish between the cases where the direct and leading object of the promise is to become the surety or guarantor of another's debt, and these where although the effect of the promise is to pay the debt of another, yet the leading object of the undertaker is to subserve or promote some interest or purpose of his own."
82In Roser v. Rozer, 2 Vent. 36, an action of indebitatus assumpsit was brought for goods sold and delivered to J. S. at the request of the defendant and for which the defendant promised to pay. The court arrested judgment, saying: "Admitting there were a promise; yet it being collateral it did not make a debt, but should have been brought as an action upon the case." In Sands v. Trevilian, Cro. Car. 107, 194, A desired B to be attorney for J. S. and undertook to pay him his fees, and such fees as he should give to counsel. Debt was brought and the plaintiff obtained judgment in the lower court, but on writ of error to the King's Bench it was held that no action of debt would lie. Professor Ames thus comments on these eases: (Cases on Suretyship, page 9, n.) "But in Haines v. Finch, Alleyn 6, Rolle, C. J., who had been of counsel for the plaintiff in Sands v. Trevilian, is reported as saying of that case that 'the judgment was not reversed upon the roll, and his opinion was that the judgment was good.' In Ambrose v. Rowe, 2 Show. 421, Skin. 217, s. c, Lord Jeffries, C. J., said,' that he thought Rolle's argument in that case of Sands c. Trevilian not promises as distinguished from debts are always promises to be answerable only on default of a principal debtor, there seems no reason to doubt that an absolute promise of a surety to pay the debt of one who received the quid pro quo and who also was absolutely liable, is a collateral promise, with reference both to the action of debt and to the Statute of Frauds.83
At the present day the use of the terms original and collateral is not very helpful because they are not clearly defined. But it is well to remember that the early adoption of these words as defining the cases which Parliament intended to fall within or outside the statute must have been based on the assumption that the old distinction between debt and assumpsit was the equivalent of the new distinction introduced by the statute. One who bears this in mind will recognize that an original promise should not be treated as necessarily implying priority in time; and that a collateral promise does not mean necessarily a promise conditional on the default of another.