William James, in his lectures on exceptional mental states, referred to the trances of mediums who channel voices and images of the dead, and of scryers who see visions of the future in a crystal ball. Wheather the voices and visions in these contexts were veridical was less of a concern to James than the mental states which could produce them. Careful observation convinced him that mediums and crystal gazers were not usually conscious charlatans or liars in the ordinary sense, nor were they confabulators or phantasm. They were, he came to feel, in altered states of consciousness conducive to hallucinations - hallucinations whose content was shaped by the questions they were asked. These exceptional mental states, he thought, were achieved by self-hypnosis, no doubt facilitated by poorly lit and ambiguous surroundings and the eager expectations of their clients.