Religion is one of the more controversial concepts in social science. It is often used to sort cultural types, but the enormous diversity of practices that people claim are religious raises a number of philosophical issues about whether one can correctly define this concept as a social taxon with necessary and sufficient properties.
One problem is that different cultures have very different views of what is and is not a religion. A common view is that a religion requires belief in supernatural beings or at least in a creator god. It also usually involves a moral code and a belief in afterlife, reincarnation or nirvana. It often involves a centralized group that has sacred texts, sacraments, rituals and symbols.
Anthropologists, who study how human beings interact with their environment, have suggested that religion developed as early protective systems for uncontrollable parts of the world such as weather and pregnancy and birth. They believe that humans tried to control these natural forces through two different means: manipulation, which they called magic; and supplication, which they called religion.
It is not unusual for philosophers to approach a contested concept such as religion by examining how many characteristics it has in common with other concepts that are well-defined. This approach, called a polythetic approach, is somewhat similar to the way scientists sort biological strains by looking at their bacterial properties. The polythetic approach may be criticized for being too broad or even irrelevant to the purpose of defining religion, but it can lead to surprising discoveries about patterns within the class and the co-occurrence of specific properties.