Ordinarily, courts evaluate the adequacy or fairness of consideration even if the consideration is legally sufficient. A promise to do what one already has a legal duty to do is not legally sufficient consideration under most circumstances. Promises made with consideration based on events that have already taken place are fully enforceable. Rescission is the unmaking of a contract so as to return the parties to the positions they occupied before the contract was made. A promise has no legal value as consideration. A covenant not to sue is an agreement to substitute a contractual obligation for some other type of action. Consideration is the value given in return for a promise. Promissory estoppel may prevent a party from using lack of consideration as a defense. The doctrine of promissory estoppel requires a clear and definite promise. Dwight offers to buy a book owned by Lee for $40. Lee accents and hands the book to Dwight. The transfer and delivery of the book constitute performance. Is this performance consideration for Dwight's promise