2. Legal duties :
    Whenever legal rules require or prohibit  certain conduct, the notion of duty has application. The plainest examples of such requirements and prohibitions are the duties created by the criminal law when it provides for the punishment of certain forms of conduct. The duties, it thus create may be either negative (e.g., to abstain from murder or theft) or positive (e.g., to report for military service or pay taxes).....

3. Obligation and duty:
    By jurists of some systems, mainly those descended from Roman law, a distinction is drawn between obligation and duty, the former being reserved for cases such as those where a determinate person is bound as a result of some past transaction or relationship to pay or render some service to another determinate individual who has a corresponding legal right to such payment or service. Obligations are typically” incurred” or created by a man for himself, whereas duties “ arise” from his position under the law without any act on his part.

4. Duties and sanctions :
    Many, perhaps most, legal theorists have argued that legal and moral duties can only be distinguished by the provision made by legal rules for coercive sanctions. However, it is conceptually impossible to hold
(1) that moral duties may be extinguished by legislative repeal or fiat, as legal duties can,
(2) that moral duties may relate to activities which are not considered in any way important as some legal duties may be, and
(3) that general moral duties could be expressly created simply for the purpose of advancing some specific objective or social aim as general legal duties frequently are furthermore, lawyers and jurists sometimes use the expression “Duty” of actions where no sanction is provided. The coercive sanctions  of the law may then be more illuminatingly regarded as the characteristic, but not invariant, legal form of this wider notion.

5. Moral duties:
    In considering moral duties, it is important to distinguish the accepted or conventional positive morality of an actual  social group from the moral principles and ideals which may govern an individual’s life but which do not exist as a shared code of a social group. The duties of positive morality are those forms of conduct (negative or positive) which like a debt are, according to the rules of the accepted moral code, held to be justifiably exacted or demanded from individuals.......

Duty in other social contexts :
    Legal and moral rules are of course not an exhaustive dichotomy, and the notion of duty also refers to the requirements of rules which fall into neither of these two categories (e.g., the rules of voluntary associations like clubs or business organizations, rules governing activities for which there are only intermittent opportunities such as ceremonies, or activities like games which are held to be voluntary and from which withdrawal is permitted).
Broadly speaking, the notion of duty or, sometimes, obligation may be used where there is a relatively enduring office or social role in which the occupant performs a specific function calling for specific forms of behavior. Thus, it is common to speak of the duties of a host or of the captain of a team or the chairman of a committee, where rules which are neither legal nor moral, specify the forms of behavior required.