Religions are a major factor in human life and have been for all time some of the most important forces shaping knowledge, the arts, and technology. Yet, they are among the most difficult and vexing subjects to study. When scholars of various disciplines, such as history, philology, literary criticism, psychology, sociology, and anthropology, attempt to examine them, they frequently encounter an impasse. They are not in agreement about the proper method of study, and they are often at odds over the definition of religion. The search for a universally adequate conception of religion can lead quickly to a minimal notion of the subject, a sort of lowest common denominator that would rank different religions as so many species under a single genus, which would be an unacceptable standard for a discipline devoted to empirical research.

The question of the correct characterization of religion is fundamental for any academic study of the subject. This issue has been a source of much controversy, with some advocating a monothetic approach and others a polythetic approach. Monothetic approaches focus on specific aspects of religion or the way in which a religious person acts, while polythetic approaches are more concerned with how a subject is classified in general terms and have a more holistic view.

Those who support a monothetic approach to the problem of religion argue that it is essential to distinguish between an ordinary human interest in God and an extraordinary interest in God. The former is characterized by a recognition of a Divine personality behind and in the forces of nature, an all-powerful Being on whom man is aware of being dependent and in whom he finds his ultimate salvation. It is an interest that makes man willing to subordinate his own interests in his daily life to those of God, and that leads him to seek virtue and to perform good works.

In contrast, those who advocate a polythetic approach to the problem of the definition of religion argue that attempting to narrowly define the concept by limiting it to such features as belief in a supreme being or the recognition of divine commands would exclude many people from its category. These people are not necessarily atheists or agnostics, but rather those who have no beliefs of a particular type and who do not exhibit certain behavioral characteristics, such as the habit of observing sacraments or keeping moral commandments.

A polythetic understanding of the term religion allows for an examination of different types of practices, and a comparison of their effects on human beings. It also enables us to see how the senses of the concept have developed over time. It is also possible to discuss two philosophical issues raised by the use of the concept of a social genus to categorize such a broad class of human activities: (1) whether one can understand this classification in terms of essential and sufficient properties, and (2) whether it is better to treat the idea of a religion as a family resemblance concept or a necessary and sufficient concept.