The philosophy known as Spiritualism is based on the simplistic premise that man is a dual being; consisting of a physical and spiritual component. The physical element (the body) disintegrates at death, but the spiritual (the "soul", "spirit", personality, consciousness, etc) continues exactly as it was, only in another form of existence: the "Spirit-world" or heaven.
The Spiritualists further claim that communication between the disincarnate and the living is possible through a human "medium" or "clairvoyant". Usually there is also a practical emphasis on healing. All Spiritualists are vaguely Christian in that they consider Jesus as some sort of great teacher or divine being, but none are dogmatically or fundamentalistically so.
