The double, at its most basic, is a duplicate of an individual or a part of a divided individual. A. E. Crawley suggests that the sources of the double, as a term, are the "mathematical ideas of multiplication and division," the "main connotation of the term" being the doppelganger, visible or invisible, material or spiritual. The source of the double as a phenomenon of duplication may be the "twin-cult," versions of which were discovered by anthropologists in primitive cultures in Africa, Asia, Europe, and the Americas, according to James Rendel Harris. The source of the double as a concept of division is located by Freud in the idea of an immortal soul, an idea rising, according to Freud, from infantile narcissism or primitive superstition. The source of the double as a concept of division was located, by Carl Jung, much further back than the infantile or primitive.