On what occasions do we commonly find a mind conversing with another mind not on the same plane with itself?--with a mind inhabiting in some sense a different world, and viewing the environment with a difference of outlook greater than the mere difference of character of the two personages will account for? The first instance of this sort which will occur to us lies in spontaneous somnambulism, or colloquy between a person asleep and a person awake. And observe here how slight an accident allows us to enter into converse with a state which at first sight seems a type of incommunicable isolation. "Awake, we share our world," runs the old saying, "but each dreamer inhabits a world of his own." Yet the dreamer, apparently so self-enclosed, may be gently led, or will spontaneously enter, into converse with waking men. The somnambulist, or rather the somniloquist--for it is the talking rather than the walking which is the gist of the matter--is thus our first natural type of the _revenant_. And observing the habits of somnambulists, we note that the degree in which they can communicate with other minds varies greatly in different cases. One sleep-waker will go about his customary avocations without recognising the presence of any other person whatever; another will recognise certain persons only, or will answer when addressed, but only on certain subjects, his mind coming into contact with other minds only on a very few points. Rarely or never will a somnambulist spontaneously notice what other persons are doing, and adapt his own actions thereto. Next let us turn from natural to induced sleep-waking, from idiopathic somnambulism to the hypnotic trance. Here, too, throughout the different stages of the trance, we find a varying and partial (or elective) power of communication. Sometimes the entranced subject makes no sign whatever; sometimes he seems able to hear and answer one person, or certain persons, and not others; sometimes he will talk freely to all; but, however freely he may talk, he is not exactly his waking self, and as a rule he has no recollection, or a very imperfect recollection, in waking life of what he has said or done in his trance. Judging, then, from such analogy as communications from one living state to another can suggest to us, we shall expect that the communication of a disembodied or discarnate person with an incarnate, if such exist, will be subject to narrow limitations, and very possibly will not form a part of the main current of the supposed discarnate consciousness. These preliminary considerations are applicable to any kind of alleged communication from the departed--whether well or ill evidenced; whether conveyed in sensory or in motor form.