“Upon rare occasions the spirits are able to subdue and control these soulless beings, which are ever ready to assume pompous names if left to themselves, in such a way that the mischievous spirit “of the air”, shaped in the real image of the human spirit, will be moved by the latter like a marionette, and unable to either act or utter other words than those imposed on him by the “immortal soul”.
But this requires many conditions generally unknown to the circles of even spiritualists most in the habit of regularly attending seances. Not every one can attract human spirits who likes.
One of the most powerful attractions of our departed ones is their strong affection for those whom they have left on earth. It draws them irresistibly, by degrees, into the current of the Astral Light vibrating between the person sympathetic to them and the Universal Soul.
Another very important condition is harmony, and the magnetic purity of the persons present.”
H. P. Blavatsky
The Mark Of God: Understanding Your "I AM Presence" 