Religion is one of the most complex and powerful human phenomena. It has shaped culture and history in all places and times, often in collaboration with or in antagonism with government power. Its importance and pervasiveness make it a central object of study within the academic field of Religion.

A number of people have offered definitions of religion, but they often fail to account for the vast range of practices that are said to be included in this social taxon. It is often thought that a definition of religion must include some kind of belief in gods or supernatural beings, but this is not necessarily the case. There are plenty of religions that do not have such beliefs. Durkheim’s functional definition of religion focuses on the way that a group creates solidarity, and Paul Tillich’s version identifies the prevailing values that provide orientation in life.

These definitions are called monothetic because they operate with the classical view that every phenomenon accurately described by a concept will share a defining property. The more recent attempts to outline a set of dimensions that distinguish religions from other phenomena are called polythetic. They move away from the classic model and treat religion as a family resemblance concept rather than a category with necessary and sufficient properties. This is an important change, but it raises a number of philosophical issues that are similar to those raised when attempting to define concepts such as democracy or literature.