Condictio indebiti


In Roman law and the Civil [law (legal system)|civil legal systems] descending from it, the condictio indebiti is a legal action whereby a plaintiff may recover what he has paid the defendant by mistake; such mistaken payment is known as solutio indebiti. This action does not lie
  1. if the sum was due ex aequitate, or by a natural obligation;
  2. if he who made the payment knew that nothing was due, for qui consulto dat quod non debet, praesumitur donare.
The action is extant in civil or hybrid law regimes, e.g. Norway, South Africa and Scotland.