Buddhists have schematized the possible life realms into six main categories: The realms of the Gods,
of the Antigods, of the Humans, of the Animals, of the Hungry Ghosts/Pretans, and the realms of Hell.
 
 
  

The "Six realms of migration" are graphically represented everywhere throughout Tibet and elsewhere in the Buddhist world in the "wheel of life" often found on temple walls. This figure represents the experience of the dying person, who flies into the "mouth of Death" (the deity Yama, holding the wheel in mouth and ands and feet), and lands on the wheel of egocentric life according to his or her evolutionary momentum. 
    The Book of Natural Liberation presuposes this cosmological context as the setting for the
                 deceased person's journey through the between. Once one has felt the boundless                  interconnectedness of all life forms, the inspiring infinite horizon of positive evolution
                 toward Buddhahood is accompanied by the terrifying infinite horizon of negative evolution                  or degeneration toward the animal, pretan, or hell-being life forms. The horrid states are                  truly frightening and definitely to be avoided. Nothingness would be far preferable.                  Awareness of the possible horrid states is a powerful motivator toward positive                  development for oneself, and an intense catalyst for compassion for others. It is                  indispensable for developing the messianic drive to save other beings from suffering that is                  called the will to, or spirit of, enlightenment. This is the spiritual conception that changes an                  ordinary egocentric being into an altruistic bodhisattva. Some Asian teachers have said in                  recent decades that the horrid states are simply metaphorical and not to be taken literally,                  that they merely indicate states of mind to be avoided.