MEDIUMSHIP: GENERAL CLASSIFICATIONS
Excerpt From "The Medium's Book" Chapter XVI #187 and #188
Two Principle Orders | Varieties Common to All Types of Medianimity
Natural or Unconscious Mediums : Those who call forth the phenomena spontaneously, without any action of their will and, for the most, part unconsciously.
Voluntary Mediums : Those who have the power of calling forth the phenomena at their will, though they are ineffective if the spirits are unwilling to cooperate).
(Kardec, "Medium's Book", Ch XVI #187)