In what form must a contract exist for one party to promise to pay the debt of another?

In California, as well as under the general principles of contract law, a promise to pay the debt of another must be in writing due to the Statute of Frauds. This legal doctrine requires that certain types of contracts, including promises to answer for the debt or default of another, must be memorialized in writing to be enforceable. The key purpose of this requirement is to prevent misunderstandings and fraudulent claims that could arise from unrecorded verbal agreements.

A verbal agreement, while it may carry weight in many situations, does not meet the requirements set forth by the Statute of Frauds for third-party debt promises. This differentiates deals based on what they pertain to; for example, contracts for the sale of goods over a certain amount, real estate transfers, and guarantees of another's debt all necessitate a written form to ensure clarity and legal enforceability.

Thus, only option B, which states that the promise needs to be in writing, aligns with legal requirements and principles governing contract law regarding a promise to pay someone else's debt. Other forms, such as oral agreements or verbal confirmations, lack the necessary legal foundation to hold up in court for this particular kind of obligation.