| As a paradigm of legal philosophy, legal duty is the foundation-category, just like the legal right. In the foundation-category, the concept of the legal right is widely studied. Compared, the study of legal duty is often ignored. So, it is necessary to study legal duty widely and deeply. This paper is trying to study legal duty, and has four parts altogether.Part one explores the concept of legal duty from the origination of duty, the paraphrase of legal duty about occidental scholar, the explanation of legal duty on academia in our country, and the descriptive interpretation of legal duty of his own: legal duty is some certain action that relevant subject ought to take under certain circumstances which is prescribed by law or stipulated by the parties and is guaranteed by the pre-established legal responsibility.Part two is that the auther analylized the constructive factors of legal duty. Affected by a developing and dynamic point of view, the author thought that legal means "ought to be ", legal duty exists in the expectation of people; thus, the goal of legal duty is to regulate people's behavior. Therefore, legal duty should exist not only in the expectation, but also in the realization of people's behavior. Its realization is the behavior mode transformation from expectation to realization. However, not all people want to carry out his legal duty, which may exist during the whole course of human society. That's the departure from behavior mode, which should not be ignored. Last, for the behavior departure, legal duty will raise the possibility of legal responsibility. So, to confirm whether a legal duty exists, we have to ensure if the three factors -should,behavior and the possibility to raise legal responsibility -exist contemporarily.Part three is to discriminate between legal duty and moral duty. The one hand, the part explores the difference between legal and moral duty from the means of realization, the route of creation, the demand of deliberate factor toward behavior and the degree of importance. On the other hand, the part sums up the relation between legal and moral duty from unification of internal and external demand, basic accord of effect, and mutual pervasion and restriction.Part four narrates the reason of performing legal duty. Performing duty on people is mostly based on three reasons: The first is that right should be equal; the second is social division and cooperation, mutual expectation and faith; the third is the restriction of responsibility. In a word, people performing legal duty is for carrying out their rights. |