A good example of the former branch of the proposition is to be found in a Massachusetts case.  The plaintiff refused to let certain wood be removed from his land by one who had made an oral bargain and given his note for it, unless he received additional security.  The purchaser and the plaintiff accordingly went to the defendant, and the defendant put his name upon the note.  The plaintiff thereupon let the purchaser carry off the wood.  But, according to the testimony, the defendant signed without knowing that the plaintiff was to alter his position in any way on the faith of the signature, and it was held that, if that story was believed, there was no consideration. 1

An illustration of the other half of the rule is to be found in those cases where a reward is offered for doing something, which is afterwards done by a person acting in ignorance of the offer.  In such a case the reward cannot be claimed, because the alleged consideration has not been furnished on the faith of the offer.  The tendered promise has not induced the furnishing of the consideration.  The promise cannot be set up as a conventional motive when it was not known until after the alleged consideration was performed. 2

Both sides of the relation between consideration and promise, and the conventional nature of that relation, may be illustrated by the case of the cask.  Suppose that the [295] truckman is willing to carry the cask, and the owner to let him carry it, without any bargain, and that each knows the other’s state of mind; but that the truckman, seeing his own advantage in the matter, says to the owner, “In consideration of your delivering me the cask, and letting me carry it, I promise to carry it,” and that the owner thereupon delivers it.  I suppose that the promise would be binding.  The promise is offered in terms as the inducement for the delivery, and the delivery is made in terms as the inducement for the promise.  It may be very probable that the delivery would have been made without a promise, and that the promise would have been made in gratuitous form if it had not been accepted upon consideration; but this is only a guess after all.  The delivery need not have been made unless the owner chose, and having been made as the term of a bargain, the promisor cannot set up what might have happened to destroy the effect of what did happen.  It would seem therefore that the same transaction in substance and spirit might be voluntary or obligatory, according to the form of words which the parties chose to employ for the purpose of affecting the legal consequences.