In English law, a guarantee is a contract to answer for the payment of some debt, or the performance of some duty by a third person who is primarily liable for that payment or performance. It is a collateral contract, which does not extinguish the original obligation for payment or performance. It is rendered null and void if the original obligation fails. The liabilities of a guarantor in law depend upon those of the principal debtor, and when the principal's obligations cease the guarantor's do too except in certain cases where the discharge of the principal debtor is by the operation of the law. If, for example, a person wrongly supposes that someone is liable to them, and a guarantee is given on that erroneous basis, the guarantee is invalid by virtue of the law of contracts, because its foundation (that another was liable) failed