That which one must do, or that which can be required of one. The term carries implications of that which is owed (due) to other people, or perhaps to oneself. Universal duties would be owed to persons (or sentient beings) as such, whereas special duties arise in virtue of specific relations, such as being the child of someone, or having made someone a promise. Duty or obligation is the primary concept of deontological approaches to ethics, but is constructed in other systems out of other notions. In the system of Kant a perfect duty is one that must be performed whatever the circumstances; imperfect duties may have to give way to the more stringent ones. In another usage, perfect duties are those that are correlative with the rights of others; imperfect duties are not. Problems with the concept include the ways in which duties need to be specified (a frequent criticism of Kant is that his notion of duty is too abstract). The concept may also suggest a regimented view of ethical life, in which we are all forced conscripts in a kind of moral army, and may encourage an individualistic and antagonistic view of social relations.