The presence of certain "mediums" was required to form the link between the worlds of the living and of the dead, and Kate Fox and her sister were the first mediums. Spiritualists do not as yet claim to know what special qualities in mediums enable spirits thus to make use of them.
Most spiritualists know that much fraud in connexion with them has been discovered - frequently by spiritualists themselves - and that the conditions favourable to obtaining them are often such as favour fraud.
Spiritualists have, as a rule, sought to convince not by testimony but by ocular demonstration.
It was discovered very early in the movement that the accuracy of these communications could not always be relied on; but it is maintained by spiritualists that by the intelligent exercise of the reason it is possible to judge whether the communicating intelligence is trustworthy, especially after prolonged acquaintance with particular intelligences, or where proofs are given of identity with persons known to have been trustworthy on earth.
This view has, however, made but little way in England and America, where the opinions of the great majority of spiritualists vary from orthodox Christianity to Unitarianism of an extreme kind.