According to Plato, debating the nature of the human soul was the most popular topic amongst philosophers. A comparison of some of the soul theories that were around during his era explains why. Different schools of thoughts and religious cults had vastly contrasting ideas about spiritual matter and what happened to it after a physical body died. To get a snapshot, the following is a brief rundown of how Hindu, Egyptian, Hebrew, Persian, and Greek cultures define the soul, or parts thereof, followed by an explanation of their afterlife beliefs.