2. These obligations are of two kinds 1st. Those founded on a natural right; as, the obligation to be charitable, which can never be enforced by law. 2d. Those which are supported by a good or valuable antecedent consideration; as, where a man owes a debt barred by the act of limitations, this cannot be recovered by law, though it subsists in morality and conscience; but if the debtor promise to pay it, the moral obligation is a sufficient consideration for the promise, and the creditor may maintain an action of assumpsit, to recover the money. 1 Bouv. Inst. n. 623.