Religion is a concept used to sort sets of social practices into categories (a kind). Since the 19th century, it has become an object of study within several disciplines, including archaeology, history, and anthropology. The study of religion has encountered a number of philosophical issues that have raised doubts about the concept itself, and about its value for understanding cultures.
A few people have proposed substantive definitions of religion, such as Edward Tylor’s minimum criterion of belief in spiritual beings or Paul Tillich’s ultimate concern. Such single-criterion, monothetic definitions of religion are criticized for their inability to distinguish all instances that deserve the label from those that do not.
Other scholars have rejected substantive definitions of religion, and instead opted for functional definitions that define membership in the category in terms of a particular role that a form of life can play in one’s life. Emile Durkheim, for example, defined religion as whatever system of practices unite a group of people into a moral community, and Paul Tillich defined it as a person’s dominant concern that organizes his or her values.
A more controversial argument against the use of substantive definitions of religion is that they are unscientific because they focus on beliefs and thus exclude the influence of psychological phenomena, such as mental states. This view is criticized because it is not obvious that the influence of psychological factors is irrelevant to the nature of a religion, and because it suggests that religious beliefs are nothing more than socially shared mental states.