been completed (or "used") at the time the next promise is made. In Roscorla v Thomas, Roscorla had contracted to buy a horse from Thomas for £30. After the sale, Thomas promised Roscorla that the horse was sound; the horse turned out to be vicious. It was held that Roscorla could not enforce the promise, as the consideration given for entering into the contract to buy the horse had been completed by the time the promise was made; in a sense, the consideration was "used up". The rule that past consideration is not good consideration is subject to the exception discussed by the Privy Council in Pao On v Lau Yiu Long. In that case, their Lordships held that past consideration can be good consideration where: The promisee performed the original act at the request of the promisor; It was clearly understood or implied between the parties that the promisee would be rewarded for the performance of the act; The actual promise made, if made before the promisee provided the consideration, must be capable of being enforced, in other words giving rise to a legally binding contract. Illusory consideration There must be some kind of connection between a promise and the consideration offered to support the promise. It is no consideration to "refrain from a course of conduct which it was never intended to pursue". The consideration must have been at least an inducement to enter into the promise. Forbearing to sue Callisher v Bischoffsheim, forbearance to sue in a groundless action still good consideration; honest mistake. Privity A promise is enforceable if it is supported by consideration, that is, where consideration has moved from the promisee. For example, in the case of Tweddle v Atkinson, John Tweddle promised William Guy that he would pay a sum of money to the child of William Guy, and likewise William Guy promised John Tweddle that he would pay a sum of money to the child of John Tweddle, upon the marriage of the two children to each other. However, William Guy failed to pay the son of John Tweddle, who then sued his executors for the amount promised. It was held that the son could not enforce the promise made to his father, as he himself had not actually given consideration for it - it was his father who had done so instead. The son didn't receive any consideration, so he cannot