13. If the debt is evidenced by a note or other written evidence, cancellation and return of the written evidence
cancels the debt.
14. Performing or promising to perform what one is already obligated to do is a valid consideration.
15. If the supposed consideration consists merely of a promise to do what one is already legally obligated to do,
consideration is invalid.
16. When a new contract is replaced with an old one, it is mandatory for the added features to be equal for both
parties for the contract to be enforceable.
17. When charitable enterprises are financed by voluntary subscriptions of many people, the promise of each
person is generally not held to be enforceable.
18. Pledges made by people to charitable associations have no binding power by law.
19. The Uniform Commercial Code states that when a contract for the sale of goods is modified by agreement
of the parties, consideration is necessary to make it enforceable.