Duties are present in many aspects of life, from religion and the military to work and home life. Subordinates have duties set by their superiors and children by their parents. Particularly in a moral sense, duties may entail a relinquishment of self-interest. Philosophers have disputed the concept of duty, disagreeing as to whether individuals decide on their own conditions. Some philosophers reject the idea of a moral duty completely.
The word "duty" can also have the definition of "that which is due" where it refers to any type of payment.
Supererogation originally only referred to religious acts. The first use of supererogation is in the New Testament of the Bible, in reference to the Good Samaritan, as an example of something morally good but not obligatory. The definition didn't appear as a nonreligious ethical theory until J.O. Urmson's "Saints and Heroes" in 1958. Some philosophers debate whether it is possible for an act to be morally good while not morally necessitated, which would invalidate supererogation.
The Roman Catholic Church defines acts of duty that surpass the requirements set by God as "works of supererogation" or "acts of supererogation." They give, as an example, 1 Corinthians 7:38: "So then, he who marries the virgin does right, but he who does not marry her does better." Here, Saint Paul states that, although people commit no moral sin by marrying, they take the moral high ground if they refrain.
In Islam the difference between a duty and a supererogatory act is clearly distinguished. Muslims must carry out a minimum number of prayers daily as a duty to their religion. Performing nafl prayers (more than required) becomes a supererogatory work. Other nonobligatory acts exist in Islam, such as additional fasting or giving sadaqa, meaning voluntary charity and giving aid in any form.