In another work[18] I have traced the origin of the belief in God to the mental state of primitive mankind, and there is no need to go over the same ground here at any length. Commencing with the indisputable fact that religion is something that is acquired, an examination of the state of mind in which primitive mankind faced, and still faces, the world, led to the conclusion that the idea of god begins in the personification of natural forces by the savage. The growth of the idea of God was there traced back to the ghost, not to the exclusion of other methods of god making, but certainly as one of its prominent causes. I must refer readers to that work who desire a more extended treatment of the god-idea. [18] _Theism or Atheism_, Chapter 2. What remains to be traced here, in order to understand the other factor that is common to religions, is the belief in a continued state of existence after death, or at least of a soul. It has been shown to the point of demonstration by writers such as Spencer, Tylor, and Frazer, that the idea of a double is suggested to man by his experience of dreams, swoons, and allied normal and abnormal experiences. Even in the absence of evidence coming to us from the beliefs of existing tribes of savages, the fact that the ghost is always depicted as identical in appearance with the living person would be enough to suggest its dream origin. But there are other considerations that carry the proof further. The savage sees in his dreams the figures of dead men and assumes that there is a double that can get out of the body during sleep. But he also dreams of dead men, and this is also proof that the dead man still exists. Death does not, then, involve the death of the ghost, but only its removal to some other sphere of existence. Further, the likeness of sleep itself to death is so obvious and so striking that it has formed one of the most insistent features of human thought and speech. With primitive man it is far more than a figure of speech. The Melanesians put this point of view when they say, "the soul goes out of the body in some dreams, and if for some reason it does not come back the man is found dead in the morning." Death and dreaming have, therefore, this in common, they are both due to the withdrawal of the double. Hence we find a whole series of ceremonies designed to avert death or to facilitate the return of the double. The lingering of this practice is well illustrated by Sir Frederick Treves in his book, _The Other Side of the Lantern_. He there tells how he saw a Chinese mother, with the tears streaming down her face, waving at the door of the house the clothing of a recently deceased child in order to bring back the departed spirit.