There are roughly 6.2 billion people in the world today and most would declare themselves religious in some way. Religion is defined as a set of beliefs, attitudes, and behaviors that provide moral guidance, a basis for belief in a higher power, and a connection to a tradition. People who regularly attend religious services also appear to be healthier than those who do not.
However, the definition of religion varies across scholars. Some scholars, like Talal Asad in his Genealogies of Religion (1993), have taken a classical approach to the concept, holding that a religion must have certain defining properties to be categorized as such. Others, including Rodney Needham in his book Sorting Things Out: A Guide to the Study of Concepts (2008), have taken a polythetic view. In a polythetic approach, a category-concept has many different possible characteristics and it is only when enough of those features co-appear to a sufficient degree that a given entity can be characterized as belonging to the category.
Polythetic approaches are growing in popularity as more and more scholars reject the idea that a social taxon, such as religion, has an ahistorical essence. This article explains how the definition of religion has evolved over time and then considers two philosophical issues that arise for this particular taxon, issues that are likely to occur for any abstract concept used to sort cultural types. The issues are: how to determine what a religion is and whether it makes sense to treat religion as a family-resemblance concept rather than a class of a single type.