A more thorough explanation:

Definition: Adpromission (ad-prə-mish-ən) is a type of suretyship contract in Roman law. It means that a person promises to be responsible for a debt owed by someone else, but only up to the amount of the debt. There were three types of adpromission in Roman law: sponsion, fidepromission, and fidejussion. Other types of contracts, such as mandatum and pactum de constitutio, could also be used as guarantees.

Example: If John borrows $100 from a bank and his friend Jane signs an adpromission contract, she is agreeing to pay the bank up to $100 if John cannot repay the loan. However, if John only owes $50, Jane is only responsible for that amount.

Explanation: This example illustrates how adpromission works. Jane is acting as a surety for John's loan, but she is only responsible for the amount he owes. If John can repay the loan, Jane does not have to pay anything. If he cannot repay the full amount, Jane is only responsible for the remaining balance.