The term, mores, introduced by the US Sociologist William Graham Sumner, can be understood as the norms which are very strictly enforced due to their importance in maintaining the well being of the group. They are considered essential to the core values of the society, so widely observed and have great moral significance. As they are thought to maintain welfare and bring prosperity to society, deviation from them is a loss for the society. Without them, a society is believed to become weak, and the social structures, fragile. These are more specifically stated and hence are more effective.
Since mores deals with higher values of people, violating them threatens those values. In order to protect those values, there is some kind of a norm, rule, or law that goes along with it to ensure its effectiveness. They help in classifying and deciding the values of right and wrong and form the instruments of social control. They are deeply rooted in society such that they hardly change. They include repugnance for societal taboos, contribute in the creation of legislation in order to prohibit those taboos and help in giving proper direction to the actions of the people by making them aware of what the norms of the society are needs to be followed compulsorily. For instance, to not harm anybody is a more, and person who harms another person is not following the more, hence can be punished. These are often created due to religious influence as well, e.g. among the Muslims, it is a more to practice purdah system, where the religious belief that women are only allowed to expose their eyes need to wear the veil in front of other males except her father and husband.
Although mores are not written down and are informal, their violation is accompanied by severe punishment and can even result in societal or religious exclusions. Such violation in a society can be of many types, such as stealing things from others, engaging in sexual relations before marriage, etc. Incidents where mores of a society are violated causes unrests among the public. Since they are not written down formally, it is often the people who punish the violator.
Mores emerge through group interaction. The people learn these norms within their group lives and seek direction to their activities with their help. These are formed within the groups become so important with a time that many times they touch the border of law. People feel strongly about the more prevalent in society and believe that without them the society would collapse. They are often considered similar to folkways. However, they differ in some degree. While mores are stricter and require more conformity, folklores are not so strict. R. M. MacIver and C. H. Page view that folklores become mores once they incorporate within themselves, the ideology of group welfare, standards of right and wrong, the sense of what is appropriate or conducive to wellbeing, etc.