摘要： 自然债务的外延应当从本国实定法和概念功能两个角度入手予以合理界定。从发生原因上看，自然债务包括法定自然债务和意定自然债务，而赌债等形态则不构成自然债务。性质上看，自然债务既不属于民法中的“非债”，也不属于法外空间，而是一种法律上的民事债务。自然债务的效力体系可以缺乏强制执行力作为推论的出发点展开：静态效力上，自然债务同时也欠缺私力救济力，且自然债权无法作为主动债权而有效主张抵销；动态效力上，自然债务受履行障碍法规制的限度取决于第二性给付义务的目的；自然债务的履行与履行允诺在必要时受债权撤销权和代位权的限制；自然债权在债之保全制度中受行使和效果的限制。

关键词: 自然债务, 法律债务, 形成体系, 效力体系

Abstract: The extension of natural obligation ought to be identified by the perspective of positive law and the function that the concept itself possesses. On this point of view, the legal natural obligation and contractual natural obligation are two patterns of natural obligation, while the obligation stemming from gambling and someother instances are not parts of them. Natural obligation belongs neither to “Nicht-Schuld” nor free space out of law. It’s a fundamental pattern of obligation in civil law. The“subjective theory”, which regards it as amoral obligation, has no persuasive foundation in positive law. The realization of the function of the conceptthe natural obligation is also impossible. The legal effects of natural obligation base on its unenforceability. Inits static legal-effects, the creditor of natural obligation could not proceed to execution under self-remedyand initiative offset with debtor. To the question of dynamic legal-effects, the limits of the remedies for non-performance rest with the purposes of secondary performance. The performances and its promises of naturalobligation are limited by the subrogation rights and right to cancel, whilst the exercise of subrogation rightsand right to cancel of creditor of natural obligation are also limited. The warrant of natural obligation is possible, whereas the retention for the natural obligation is impossible.

Key words: Natural Obligation, Legal Obligation, Making System, Legal-Effects System