A shaman, sometimes called a witch doctor or medicine man (women can also be shamans and some evidence suggests they originated the practice), is one who uses his or her mastery of life-forces of the world in order to provide a service to fellow tribesmen or to enhance his or her own powers.
In general, shamanism is based on a belief that all things in the world are alive and whatever happens in the world is due to the behaviour of life-forces. Shamans have the special abilities to influence or control these forces in such a way as to mediate between them and humans. Often they do this through a "vision quest" in which they communicate with these life-forces and travel to parts of the cosmos in the heavens or under the earth that are closed to others.
They have derived their own powers from those that pervade the world, usually as a gift from a superhuman power who becomes a helper, guardian, and guide to the shaman. A large bird, bear, wolf, or other large animal is usually this guardian. Shamans serve as a conduit, an intercessor, between the world powers and their people who depend on these powers and thereby depend on their shamans for their survival. Shamans foretell the future and see what is happening in distant places. They cure sickness, escort the dead to the afterlife, foresee the best hunting places, stave off malevolent forces, and engage in numerous other functions.
The above description best fits Siberian and North American shamans that serve as the prototype, but some of these characteristics are found around the world.
Recently, some scholars have argued that the term shamanism should not be used so widely, because it makes diverse practices appear homogeneous and this includes Australian Aborigines. Yet in Australia specially qualified Aborigines go on vision quests, often on a string, a rope, a bird, the back of a snake, or the rays of the setting sun; and they provide services to their people. Some use magical crystals to obtain X-ray vision or control a life-force.
In Arnhem Land, Southwest Australia, and Kimberley they obtain power from the rainbow or water serpent, both connected to the sky. In Australia a central feature of producing a shaman involves a functionary such as a sky hero who inserts a magical substance such as quartz into his or her body.
Some of the Aboriginal belief system involves cult totems, that is, rituals around some ancestral figure such as a sky hero or an animal and in some parts of the world occasionally a plant or other object. The Aborigines engage in rituals which record the deeds of ancestors and heroes in connection with rock sanctuaries associated with the deeds. The heroes are totems and have bird or terrestrial animal names. For some of the Aborigines, the ancestors are not human heroes but birds or animals. Some ceremonies are a re-enactment of the creation acts of the past and of the hero's or animal's role. They are vigorous and engrossing, involving dancing and beating sticks on the ground for timing. The singers and even those who are observers become engrossed in the ritual and enter into it. It is these totemic beliefs and practices that have induced some scholars of Aboriginal life to proclaim that the Aborigines engage in totemic but not shamanistic practices.
However, as the above description of shamanism may suggest, clear parallels with some of the features called shamanism elsewhere are also present. It would seem prudent to recognize that one can find various degrees of both and to rule out one altogether is to miss an important part of the picture. Similarly, one can find totemism among North American natives, and the distinct shamanism there does not vitiate it.
It has also been argued that Siberian shamans do not enter into "trances" but only play-act, and therefore this behavior is not a distinguishing feature of shamans. This argument overlooks extensive research in psychology extending over several decades on trance behaviors, also called ecstasy, hypnosis, possession, altered states of consciousness, etc.
Two criticisms have emerged from this research, one logical and the other empirical. The logical criticism is that "trance" is circular. The definition is not independent of what it is supposed to explain. If we ask how we would know that person is in a trance we are told that it is because of the behaviors, such as struggling with an evil force. If we ask further why that person behaves in such a fashion, we are told that it is because of a trance. The empirical evidence, both behavioral and physiological, indicates that so-called trance behavior is one of role enactment. The person carries out the role to whatever intensity he or she has the skill and the desire to imagine that role (vision quest, possession by demons, etc.). Daydreaming, so-called hypnosis, children's make-believe, and multiple personalities are similar behaviors. It is engrossed imagining, and some can do it more fully than others. Many children, some shamans, multiple personalities, and some others are very good at it.
There is no special "state" called trance but only a continuity with normal behaviors that everyone engages in. If there is a difference in the degree of role enactment or engrossed imagining of Siberians and Australians it is not one that distinguishes shamans from non-shamans but only differences in points along a continuum that all people share.
Professor Noel Wilson Smith.