The late Carl Sagan once asked the Dalai Lama what he would do if science were to cast doubt on a central tenet of Tibetan Buddhism-reincarnation. The Dalai Lama replied with a grin: “It’s going to be hard to disprove reincarnation.”
The doctrine of reincarnation is not peculiar to Buddhism. It is prominent in other eastern religions as well as in some tropical African cultures. The Pythagoreans made reincarnation a part of their metaphysics; so did Plato (who argued that it accounted for our knowledge of the Forms) and, later, Schopenhauer. It has cropped up in certain Christian heresies and in Jewish Cabbalism. In the US today, more than a quarter of the people surveyed say they believe in reincarnation.
Disproving reincarnation would shake up a lot of world views. But is such a disproof as unimaginable as the Dalai Lama thinks? One might start with a simple observation that, a century ago, the world’s population was under two billion; today it is six billion. As a matter of mathematical necessity, most people alive today cannot be re-embodied versions of people who died just before their birth.
Believers in reincarnation get around this demographic argument by surmising that the extra souls came from other species, or from elsewhere in the universe, or by allowing that new souls might be created. The important thing is that, once in existence, a soul is not destroyed by the death of a body it might inhabit.
But that raises a second objection to reincarnation. How can my self, which is so intimately bound up with the structures of my brain, survive its disintegration at death? Reincarnationists have a stock answer to this argument. The brain, they say, is like a radio. When it is damaged, the music becomes distorted. When it is smashed, the music stops altogether. But even then the radio waves are still out there to be received. A new radio can pick them up, provided it is tuned to the right frequency.
If reincarnation cannot be ruled out on empirical grounds, perhaps it can be discredited on a priori ones. Some philosophers have argued that the idea of reincarnation is incoherent. If, for example, I recall having fiddled while Rome burned, that does not mean I am Nero reborn. For me to be Nero, in this view, my body must be physically continuous with his; in other words, I would…