It is easy for a mediumistic person to have clairvoyance also, because a mediumistic person who has the same tendency of allowing himself to be obsessed by the spirit can allow the thought of another to obsess him. And in that way he can also know the thought of another. Only the difference between the clairvoyant and the medium is that the clairvoyant need not necessarily be a medium, and a medium may not be clairvoyant.