Reincarnation has a long tradition in both religion and philosophy. The basic idea is a mind or soul occupies one body and then dies. After death, the mind or soul somehow acquires another body. In theory, this could also be done scientifically, perhaps via a memory transfer from one brain to another. Of course, that raises many questions about whether the person is being transferred, copied or whatever.
Reincarnation requires the existence of bodies and non-physical minds. Aside from cases such as thinkers like Berkeley, most accept the existence of bodies. The existence of a non-physical mind is much more controversial. The reason why reincarnation requires a non physical mind could be seen as a matter of definition. If the mind is a physical entity (such as the brain) then it cannot be reincarnated because it would always be incarnate. This non-physical mind could be the soul, a Cartesian mind, or even a set of functions (as per the functionalist account of the mind) that could move from one body to another. In case you might be wondering, a brain transplant would not really be reincarnation since the person would still be “in” his or her original brain.
Religious people tend to simply assume the truth of reincarnation based on their faith. As most know, it is an essential part of Buddhism (in its various forms) and also appears in Hinduism. Some thinkers attribute this view to Christianity and Judaism as well. After all, on Judgment day the dead are supposed to rise again in the flesh.
Interestingly enough, a 2003 Harris poll (see page 14 of the January 28 Newsweek) indicated that 40% of American believe in reincarnation. Since many Americans are Christians, this certainly creates an interesting situation. After all, Christianity is supposed to reject reincarnation in favor of an eternal afterlife. Of course, there is the bit about judgment day and the dead rising in the flesh. Perhaps the dead hang out until judgment day and then return after the events are over.
Tom Morton, in his unauthorized biography of Tom Cruise, claims that some Scientologists hope that Suri is the reincarnation of L. Ron Hubbard (a good sci-fi writer and the founder of Scientology). The Scientologists deny this. Based on what I’ve read about Scientology, their basic metaphysics is lifted from Cartesian dualism (there is a material body and a non-material mind). Assuming this metaphysics, reincarnation would be possible-the mind could survive the death of the body and acquire a new one.
Philosophers, of course, always argue for it-we live to argue in this life and possible the next. In the Meno, Plato presents perhaps the best case for reincarnation. His most plausible argument is that Socrates claims to have found knowledge about geometry in a servant that the servant did not learn in this life. Socrates infers that the servant acquired this knowledge in another life. Hence, reincarnation is inferred to be real.
Naturally enough, there are numerous arguments against Plato’s case. Some have argued that Socrates actually provided the knowledge via leading questions. Some put forth alternative explanations. For example, such knowledge might be innate to the mind or the brain.
Aside from Plato’s argument, the evidence for reincarnation is scarce and often dubious. The main evidence people point to are cases of past life regressions, deja vu and fears people have that seem to have no basis. While amusing, this evidence is extremely weak.
Past life regressions never provide any useful information and never provide anything that could not have been learned via more conventional means-such as books or the History Channel. Of course, if someone regressed and was able to reveal the location of lost cities, to speak correctly in ancient languages they never learned in this life, or reveal some hidden historical secret, then I would lend more credence to this alleged phenomenon. Also, people who “regress” seem to be clearly led by the person they are paying to regress them. This casts the whole regression thing into even greater doubt.
Deja vu does have some appeal as evidence, but can be better explained in terms that do not involve reincarnation. For example, the feeling could be the result of having experienced something similar that one has forgotten. Also, people experience deja vu in places that are new, such as a new house, and hence did not exist prior to the person being born. Of course, there is the possibility that some cases of deja vu are legitimate memories from a previous life-but the challenge is discerning these (alleged) true memories from other (far more likely) causes.
Some have claimed that if a person has a fear that cannot be explained by a current life experience, then it must result from a past life disaster. For example, if someone is very afraid of fires, but has never been badly burned, then it is suspected they were badly burned or killed by fire in a previous life. While this has some appeal, such fears are easy to explain without dubious metaphysical theories. For example, people can be afraid of things they are aware of even though they were never hurt by them. For example, I’ve never been in a plane crash, but I fear flying. This is not a past life thing. I know planes can crash and hence my fear is based on that knowledge and the general fear of death. Such fears can also be explained in terms of psychology and neurology without bringing in the matter of past lives.
Overall, there seems to be little reason to believe in reincarnation. It could be true, but it could also be completely wrong. My own view is that it can make a neat plot device in fiction but does not seem to be adequately supported enough for me to accept it.