Definition of Pre-existence & Re-existence
What we mean by the terms "pre-existence" and "re- existence," is in short: “existence before birth," and “existence after death," respectively. Of course we take it for granted that “we exist in this world,” in the present. This is not a mere belief, to us; we regard it as a fact. To be conscious is to be conscious of “our” existence in “the world.” This “concept of existence” in time and space, seems to be built into the psychology of a human being. All societies, all cultures, all indivi¬duals accept this “existence” to be a common human experience. Therefore, it is natural to question about the past of this existence: "Did we exist in the past, before birth?" We also question about the future of existence: "Will we exist in the future, after death?” Obviously, if we did not exist in the present, we would not be asking these questions. Modern existential philosophy is based on this assumption, though the Buddha questioned it.
Mankind in every culture has speculated about these questions. Many theories have been built around them in all ages. These concepts: “pre-existence” and “re-existence” have been given different names and understood in different ways in different cultures. They have been termed resurrection, re-incarnation, transmigration, rebirth, palingenesis metempsychosis, punar-janman, punar-jathi, punabbhava, etc. etc.