The evolution of religion cannot be precisely determined owing to the lack of clearly distinguishable stages, but anthropological and historical studies of isolated cultures in various periods of development have suggested a typology but not a chronology. One type is found among some Australian aborigines who practice magic and fetishism (see fetish) but consider the powers therein to be not supernatural but an aspect of the natural world. Inability or refusal to divide real from preternatural and acceptance of the idea that inanimate objects may work human good or evil are sometimes said to mark a prereligious phase of thought. This is sometimes labeled naturism or animatism. It is characterized by a belief in a life force that itself has no definite characterization (see animism).
A second type of religion, represented by many Oceanic and African tribal beliefs, includes momentary deities (a tree suddenly falling on or in front of a person is malignant, although it was not considered "possessed" before or after the incident) and special deities (a particular tree is inhabited by a malignant spirit, or the spirits of dead villagers inhabit a certain grove or particular animals). In this category one must distinguish between natural and supernatural forces. This development is related to the emergence of objects of devotion, to rituals of propitiation, to priests and shamans, and to an individual sense of group participation in which the individual or the group is protected by, or against, supernatural beings and is expected to act singly or collectively in specific ways when in the presence of these forces (see ancestor worship; totem; spiritism).
In a third class of religion—usually heavily interlaced with fetishism—magic, momentary and special deities, nature gods, and deities personifying natural functions (such as the Egyptian solar god Ra, the Babylonian goddess of fertility Ishtar, the Greek sea-god Poseidon, and the Hindu goddess of death and destruction Kali) emerge and are incorporated into a system of mythology and ritual. Sometimes they take on distinctively human characteristics (see anthropomorphism).
Beyond these more elementary forms of religious expression there are what are commonly called the "higher religions." Theologians and philosophers of religion agree that these religions embody a principle of transcendence, i.e., a concept, sometimes a godhead, that involves humans in an experience beyond their immediate personal and social needs, an experience known as "the sacred" or "the holy."
In the comparative study of these religions certain classifications are used. The most frequent are polytheism (as in popular Hinduism and ancient Greek religion), in which there are many gods; dualism (as in Zoroastrianism and certain Gnostic sects), which conceives of equally powerful deities of good and of evil; monotheism (as in Christianity, Judaism, and Islam), in which there is a single god; supratheism (as in Hindu Vedanta and certain Buddhist sects), in which the devotee participates in the religion through a mystical union with the godhead; and pantheism, in which the universe is identified with God.
Another frequently used classification is based on the origins of the body of knowledge held by a certain religion: some religions are revealed, as in Judaism (where God revealed the Commandments to Moses), Christianity (where Christ, the Son of God, revealed the Word of the Father), and Islam (where the angel Gabriel revealed God's will to Muhammad). Some religions are nonrevealed, or "natural," the result of human inquiry alone. Included among these and sometimes called philosophies of eternity are Buddhist sects (where Buddha is recognized not as a god but as an enlightened leader), Brahmanism, and Taoism and other Chinese metaphysical doctrines.