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PROEM
The link connecting the subjects treated in this volume is their dependence upon mental states. Should it be thought that Astrology, Divination, Apparitions, and Witchcraft are based upon objective facts, it is believed that the method of their explanation will show that they are properly classified. The author has adopted certain principles as working laws: namely, that before endeavoring to explain how phenomena exist, it is necessary to determine precisely what exists; and that so long as it is possible to find a rational explanation of what unquestionably is, there is no reason to suspect, and it is superstition to assume, the operation of supernatural causes.
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