Detailed Answer
(d) A preexisting legal duty is not sufficient as consideration
because no new legal detriment is suffered by performing the
prior obligation. For example, when a creditor agrees to accept as
full payment an amount less than the full amount of the undisputed
(liquidated) debt, the agreement lacks valid consideration
to be enforceable. However, when the amount of an obligation is
disputed, the creditor’s promise to accept a lesser amount as full
payment of the debt is enforceable. Preexisting legal duties are
not valid as consideration.