Religious beliefs and practices are widespread around the world. They shape the world views of cultures from isolated tribes to vast empires, and they influence the lives of individuals within those communities. Yet they remain one of the most controversial and contested aspects of human society.

The semantic range of the concept religion has expanded and shifted over time, so that it may be difficult to determine what is and is not a member of this social taxon. Some efforts to sort out a definition of religion (e.g., Frazer 1922) have emphasized a set of elements such as belief in powers higher than human beings and attempts to propitiate or please them. Others, such as Durkheim’s (1905) definition based on the function of creating solidarity, or Tillich’s (1997) functional approach to religion, shift the sense of the term into a register that is different from the classical sense of scrupulous devotion.

These changes raise two philosophical issues for the concept of religion, issues that are likely to apply to other abstract concepts used to sort cultural types—for example, literature or democracy. The first is whether a concept can be understood as having an essence, the idea that every instance that accurately describes that concept will display a particular set of properties. The second is whether the notion of religion can be understood as a family-resemblance concept, the idea that the category to which a phenomenon belongs is best described by identifying its prototypes—that is, those examples that most closely resemble it in terms of their core features.

This article will explore these issues by considering the history of how the concept of religion has shifted and expanding, and by examining some of the current controversies surrounding it. It will also consider some of the ways that scholars have approached this issue, and conclude by presenting what might be considered a “polythetic” definition of religion—that is, a method for sorting out what is and is not a member of the class to which it belongs.

Polythetic definitions of religion are gaining in popularity because they avoid the claim that an evolving social category has an ahistorical essence. They do so, however, by allowing that there may be many properties that are common—even typical—of religions without being essential.

A number of historians and philosophers have analyzed these contrasting approaches to the definition of religion, including the German idealist Friedrich Schelling (1775-1854), who focused on mythology; the Swiss social philosopher Auguste Comte (1857-1912), who viewed it as a formative influence on human history; and the American theologian Charles E. Patterson (1889-1960), who viewed it as an aspect of human morality. This article examines these diverse perspectives, and proposes a polythetic definition of religion that is influenced by all of them. This definition will be applied to several of the most important contemporary religions, focusing on beliefs, representations, and practices. This book will be of interest to students in sociology, anthropology, history, and religion.