Civil, praetorian, and natural obligations

Like ownership (dominium) or inheritance (hereditas), obligation was also originally an exclusively civil-law concept. When a debtor was bound by the praetor, not by civil law, to do something, jurists used other Latin words or expressions (e.g., actione teneri, debere, adstringere).

obligations were established by statutes or at least sanctioned by civil law, and they were enforceable by civil actions. On the other hand, praetorian obligations, also called honorary, were established by a praetor’s own jurisdiction and were enforceable by praetorian actions, especially actions in factum.

A third category of nonenforceable obligations was natural obligations. Originally, these were obligations contracted by individuals who were under parental, marital, or dominical power: children, women in manu, and slaves. They were not enforceable obligations because persons under power could not bring an action to claim them. Just as natural possession was not enforceable by action, neither was natural obligation. Nonenforceability did not imply invalidity, however; natural obligations were valid. They were legally relevant and had legal effects. The most important effect was that if a debtor fulfilled his obligation, by law he could not bring an action to take reclaim his payment (soluti retentio) (Julianus, D. 41.1.16.4). Additionally, natural obligations could be used to offset a claim of the debtor; they could also be transformed into a new obligation (novatio), and a security could be provided to ensure its fulfillment.