Religion is a system of thought, feeling, and action which is shared by a group and which gives any member of that group an object of devotion. Usually, religion concerns itself with that which transcends the known, the natural, or the expected. It is an acknowledgment of the extraordinary, the mysterious, and the supernatural. The religious consciousness recognizes a transcendent, sacred order and elaborates a technique to deal with the inexplicable or unpredictable elements of human experience in the world or beyond it.
The evolution of religion cannot be precisely determined because of a lack of clearly distinguishable stages, but anthropological studies of primitive and isolated cultures in various periods of development have suggested some of these stages. The Australian bushman, considered to be the most primitive aborigine in the world, practices Magic and fetishism, but does not consider the powers therein to be unnatural. Inability or refusal to divide real from preternatural and acceptance of the idea that inanimate objects may work human good or evil is sometimes said to mark a prereligious phase of thought. This stage is sometimes labeled naturism or animatism. It is characterized by a belief in a life force which itself has no definite characterization.
The second stage of evolution, represented by many Oceanic and African tribal beliefs, includes momentary deities and special deities. In this stage man has distinguished between natural and supernatural forces. This development is related to the emergence of objects of devotion, to rituals, to priests and medicine men, and to an individual sense of group participation.
The third stage of development, usually heavily interlaced with fetishism (magic, momentary and special deities, nature gods, and deities personifying natural functions; e.g. the Greek sea-god, Poseidon or Ra, the Babylonian goddess of fertility, emerge and are incorporated into a system of Myth and ritual.
Beyond this suggestion of stages, the variety of religious systems and experiences does not permit of any evolutionary classification . However, theologians and philosophers agree that sophisticated religions embody a principle of transcendence, i.e., a concept, sometimes a god-head which involves man in an experience beyond the satisfaction of his immediate personal and social needs, an experience known as "the sacred" or "the holy."
In the study of comparative religions certain classifications are used. The most frequent are Polytheism, in which there are many gods, and Monotheism in which there is a single god.