A natural obligation arises from circompstances

In most legal systems, there is no legal sanctions regarding natural obligations. Implementation of this commitment depends on the will of debtor and only in this case it is irretrievable. Voluntary execution (Payment) of a natural obligation (also called an imperfect obligation), regardless of its bases which can be an aborted or a pure moral duty is, in most legal systems, considered as a valid legal act in regard of the civil creditors, and not an undue payment or an unjustified enrichment. Therefore, it cannot be restitute except if it is done involuntary or fraudulently to the prejudice of the civil creditors. As the payment of a natural debt is totally depended to debtor’s decision, its legal nature is supposed to be a unilateral legal act, and not an agreement. The French case law regarding natural obligations is contradictory but in Iran’s legal system the execution of natural obligation is valid provided that there is no malice and intent to prejudice the civil creditors