From Pythagoras to Plato, and Apart From the East

Plato took up metempsychosis and gave it its most influential Greek philosophical form, most fully in the myth of Er that closes the Republic and in the Phaedo's argument for the soul's immortality, where souls choose new lives and drink from the river of forgetfulness before rebirth, carrying moral consequences from one life into the conditions of the next.

Later Neoplatonist philosophers preserved and elaborated the doctrine as part of a broader account of the soul's descent into and ascent out of bodily existence. Comparisons to Hindu and Buddhist rebirth doctrines are common and not baseless, since both describe a soul or continuum passing through successive bodies shaped by past conduct, but historians of religion caution against treating metempsychosis as simply the Greek name for the same idea: Pythagorean and Platonic transmigration has no developed doctrine of karma as an impersonal causal law comparable to Indian systems, and unlike Buddhist rebirth it generally assumes a persisting, individual soul rather than a chain of causally linked but non identical states. Whether Pythagoras derived the doctrine from contact with Indian, Egyptian or Orphic sources, or arrived at it independently, remains a question ancient sources debate and modern scholarship cannot settle from the evidence available.