Religion shapes the lives of most people on Earth, yet it is surprisingly hard to define. This level looks at why, introduces two classic thinkers, and gives a brief, respectful outline of the world's major traditions.

Why definitions are difficult

Define religion as “belief in God,” and you leave out much of Buddhism, which in many forms does not center on a creator god, as well as traditions with many gods. Define it as “belief in the supernatural,” and you may miss religions focused mainly on practice, community and ethics rather than doctrine. Try something broader, such as “whatever gives life ultimate meaning,” and suddenly sports fandom or devotion to a political cause might count. Definitions tend to be either too narrow or too broad: they exclude traditions that clearly belong, or include things that clearly do not.

Scholars often sort definitions into two families. Substantive definitions say what religion is about: the anthropologist E. B. Tylor proposed in 1871, as a minimum, “the belief in Spiritual Beings.” Functional definitions say what religion does, such as binding communities, giving meaning, offering comfort or setting moral norms. Some scholars also point out that the category “religion” grew up in European history, and that other cultures did not always separate religious life from cultural or political life in the same way.

Durkheim: the sacred and the community

The French sociologist Émile Durkheim, in The Elementary Forms of the Religious Life (1912), defined religion as “a unified system of beliefs and practices relative to sacred things,” which unite their followers into a single moral community. His key distinction is between the sacred, things set apart and treated with special reverence, and the profane, ordinary things. Durkheim stressed religion's role in binding people together and expressing shared values. Critics say he focused so much on society that he underplayed what believers themselves say they encounter.

William James: individual experience

The American psychologist and philosopher William James, in The Varieties of Religious Experience (1902), took the opposite angle. For his purposes he defined religion as “the feelings, acts, and experiences of individual men in their solitude, so far as they apprehend themselves to stand in relation to whatever they may consider the divine.” James studied individual religious experience, such as conversion and mystical states, and judged it partly by its fruits in people's lives. Critics say he neglected the communal, ritual and institutional side that Durkheim emphasized.

Many scholars now treat religion as a cluster concept: there is no single feature that all religions share, but a set of overlapping traits, such as belief, ritual, sacred stories, moral codes, community and experience.

The world's traditions in outline

• Judaism: the covenant between God and the people of Israel, the Torah, and a rich tradition of law and interpretation; the oldest of the Abrahamic faiths.
• Christianity: faith in Jesus of Nazareth as the Christ, the Son of God; the largest religion, with more than two billion followers in Catholic, Orthodox, Protestant and other churches.
• Islam: submission to the one God (Allah), with Muhammad as the final prophet and the Qur'an as revelation; the second largest religion, with about two billion followers.
• Hinduism: a diverse family of traditions from India, with ideas such as dharma, karma and liberation (moksha); more than a billion followers.
• Buddhism: the path taught by Siddhartha Gautama, the Buddha, toward liberation from suffering through insight and ethical living.
• Others: Sikhism, founded by Guru Nanak in the Punjab; Chinese traditions such as Confucianism and Daoism; Shinto in Japan; and many Indigenous religions.

Well over a billion people describe themselves as having no religious affiliation, though many of them still hold some spiritual beliefs. This course takes all these perspectives seriously.

Worked example: is it a religion?

Try applying this level's tools to four test cases. The aim is not to reach a final verdict but to see how definitions shape answers.

• Theravada Buddhism. Many Theravada Buddhists do not worship a creator God. A definition based on belief in God would exclude it, which almost every scholar thinks is a mistake. Tylor's broader “Spiritual Beings” fares a little better, since many Buddhists honor heavenly beings, but those beings are not central. A functional definition includes it easily: monasteries, rituals, ethics and a path to liberation. On the cluster view it has nearly every trait.
• Confucianism. It centers on ethics, ritual, family and the cultivation of virtue, with ancestor veneration and reverence for Heaven. Scholars genuinely disagree whether to call it a religion, a philosophy or a way of life. Many people in East Asia combine it with Buddhist and Daoist practice without seeing any conflict.
• A devoted football club following. Fans have sacred places, rituals, songs, shared identity and intense feeling. A purely functional definition might count it. But most fans would laugh at the idea, and it lacks beliefs about ultimate reality or a moral path. This shows why functional definitions can be too broad.
• A national day of remembrance. Silence, hallowed ground, solemn ritual and a moral community: Durkheim would see the sacred at work. Sociologists sometimes use the term civil religion for such patterns.

Notice the lesson. Each definition captures something real, and each has blind spots. When you hear someone claim that a movement “is really a religion,” or that a tradition “is not a religion but a philosophy,” ask which definition they are using and why. Often the label is doing hidden work in an argument.