债体现为一种法律关系,债权人和债务人都受到法律的约束。自然之债是介于债与非债之间的中间地带。但是,仅诉讼时效期间的经过并不必然发生自然之债,债务人的抗辩是自然之债发生的必要条件。此外,不法原因给付是不能划入自然之债中的。正是基于自然之债介于债与非债直接的特性,自然之债于社会道德规范与法律规范间的过渡衔接起到了非常重要的作用。 Debt manifests itself as a legal relationship, with creditors and debtors subject to the law. Natural debt is between debt and non-debt. However, natural debt only does not necessarily occur during the limitation of action, and debtor’s defense is a necessary condition for natural debt. In addition, the unjust cause of payment can not be included in the natural debt. It is based on the direct nature of debt between debt and non-debt. Natural debt plays a very important role in the transition between social ethics and legal norms.