civil law. When the plaintiff has paid to the defendant by mistake what he was not bound to pay either in fact or in law, he may recover it back by an action called condictio indebiti. This action does not lie, 1. if the sum was due ex cequitate, or by a natural obligation; 2. if he who made the payment knew that nothing was due, for qui consulto dat quod non debetat, prcesumitur donare. Vide Quasi contract.