Which of the following statements about a modification of a contract is true?

In contract law, a modification to an existing contract typically requires consideration to be enforceable. Consideration is an essential element of a valid contract; it refers to the value or benefit that each party must agree to give or perform for the other. When modifying a contract, both parties usually need to provide some form of exchange or benefit that justifies the change to the original agreement. This means that if one party simply proposes a change without any new consideration, the modification may not be enforceable.

The other statements do not accurately reflect the requirements for modifications in most jurisdictions. A modification cannot usually be unilaterally made by one party, as this would disregard the mutual assent required in contract law. While written agreements are often favored for greater clarity and to meet statutes of fraud in certain contracts, certainly not all modifications must be in writing unless the underlying agreement, by law, requires it. Oral agreements can be enforceable, but they often face challenges in terms of proving the terms and the intent of the parties involved. Thus, the understanding that consideration is necessary for a modification to be enforceable underscores the importance of mutual exchange in contract law.