duty what a person is obligated or required to do. Duties can be moral, legal, parental, occupational, etc., depending on their foundations or grounds. Because a duty can have several different grounds, it can be, say, both moral and legal, though it need not be of more than one type. Natural duties are moral duties people have simply in virtue of being persons, i.e., simply in virtue of their nature. There is a prima facie duty to do something if and only if there is an appropriate basis for doing that thing. For instance, a prima facie moral duty will be one for which there is a moral basis, i.e., some moral grounds. This contrasts with an all-things-considered duty, which is a duty one has if the appropriate grounds that support it outweigh any that count against it.
Negative duties are duties not to do certain things, such as to kill or harm, while positive duties are duties to act in certain ways, such as to relieve suffering or bring aid. While the question of precisely how to draw the distinction between negative and positive duties is disputed, it is generally thought that the violation of a negative duty involves an agent’s causing some state of affairs that is the basis of the action’s wrongness (e.g., harm, death, or the breaking of a trust), whereas the violation of a positive duty involves an agent’s allowing those states of affairs to occur or be brought about.
Imperfect duties are, in Kant’s words, ‘duties which allow leeway in the interest of inclination,’ i.e., that permit one to choose among several possible ways of fulfilling them. Perfect duties do not allow that leeway. Thus, the duty to help those in need is an imperfect duty since it can be fulfilled by helping the sick, the starving, the oppressed, etc., and if one chooses to help, say, the sick, one can choose which of the sick to help. However, the duty to keep one’s promises and the duty not to harm others are perfect duties since they do not allow one to choose which promises to keep or which people not to harm. Most positive duties are imperfect; most negative ones, perfect.
See also DEONTIC LOGIC, KANT, RIGHTS, ROS. B.R.