Among the Greek philosophers we find that Pythagoras, Plato and their followers believed in this theory of Metempsychosis or Transmigration of souls. Pythagoras says: "After death the rational mind, having been freed from the chains of the body, assumes an ethereal vehicle and passes into the region of the dead where it remains till it is sent back to this world to inhabit some other body human or animal. After undergoing successive purgations, when it is sufficiently purified, it is received among the gods and returns to the eternal source from which it first proceeded." Plato also believed in this theory. Of course we cannot tell exactly from whence Pythagoras and Plato got these ideas. Some say that they learned these doctrines from Egypt; others believed that, either directly or indirectly, they learned the theory of transmigration from India. Plato describes in "Phaedrus," in mythological language, why and how the souls take their birth upon this plane, either as human or animal. He says: "In the heaven Zeus, the Father and Lord of all creatures, drives his winged car, ordering all things and superintending them. A host of deities and spirits follow him, each fulfilling his own function. Whoever will and can follows them. After taking this round, they advance by a steep course along the inner circumference of the heavenly vault and proceed to a banquet. The chariots of the gods, being well balanced and well driven, advance easily; others with difficulty; for the vicious horse, unless the charioteer has thoroughly broken him, weighs down the car by his proclivity towards the earth, whereupon the soul is put to the extremity of toil and effort. The souls of gods reach the summit, go outside and stand upon the surface of heaven, and enjoy celestial bliss. Such is the life of the gods; other souls which follow God best and are likest to Him succeed in seeing the vision of truth and in entering into the outer world with great difficulty. The rest of the souls longing after the upper world all follow; but not being strong enough, they are carried round in the deep below, plunging, treading on one another, striving to be first, and there, in confusion and extremity of effort, many of them are lamed and have their wings broken. Thus when the soul is unable to follow and fails to behold the vision of Truth, sinks beneath the double load of forgetfulness and vice, her feathers fall from her and she drops to earth and is born again and again as human beings or as animals." Plato says: "Ten thousand years must elapse before the soul can return to the place from whence she came, for she cannot grow her wings in less." "At the end of the first thousand years, the souls of the good and of the evil kind come together to draw lots, and choose their bodies according to their tendencies and the bent of their characters. They may take any they like. Instead of receiving the natural consequences of their deeds and misdeeds of their previous lives they are allowed to choose their own lot, according to their experience and bent of character. Some, being disgusted with mankind, prefer to be born as animals, such as lions and eagles or some other animals. Others delight in trying their luck as human beings." From this mythological description we gather what Plato meant by transmigration.

This Platonic idea of transmigration or of successive lives of those who inhabit this earth has been criticized by various thinkers of modern times; and referring to this idea the late Doctor Myers, of the Psychical Research Society of London, writes in his second volume of "Human Personality": "The simple fact that such was probably the opinion of both Plato and Virgil shows that there is nothing here which is alien to the best reason or to the highest instincts of men. Nor, indeed, is it easy to realize any theory of the direct creation of spirits at such different stages of advancement as those which enter upon the earth in the guise of mortal man. There must, one feels, be some kind of continuity—some form of spiritual past." (P. 134.) Why does He not create all souls equal? Why will one soul be highly advanced spiritually while another is entirely ignorant and idiotic? This question cannot be answered, this problem cannot be solved by the special creation theory, and therefore Doctor Myers says that there is no doubt that there was some previous continuity or spiritual past of each individual soul, and therefore he tacitly admits the theory of Transmigration. Although from a scientific viewpoint he could not give any direct proof regarding this idea of a pre-existence of the soul, still he could not deny it entirely when he said: "The shaping forces which have made our bodies and our minds what they are may always have been psychical forces—from the first living slime-speck to the complex intelligences of to-day." "The old transmigrationist's view would thus possess a share of truth and the actual man would be the resultant not only of intermingling heredities on father's and mother's sides, but of intermingling heredities, one of planetary and one of cosmic scope." ("Human Personality," Vol. II, p. 267.)

But this theory of Transmigration, as described by Plato, is a little different from a similar theory which existed in India before his time. In the Platonic idea of transmigration, as we have already seen, the souls were allowed to choose their own lot according to their experience or bent of character, but not to receive the natural consequence of their deeds and misdeeds. Plato did not say anything about the law which governs souls; but in ancient India the great thinkers and philosophers explained that each individual soul is bound by the inexorable law of nature to receive its body as a natural consequence of its former deeds and misdeeds, and not to have free choice of its lot according to its bent of character. The great thinkers and philosophers of ancient India discovered the universal law of cause and effect, of action and reaction, and called it by the Sanskrit term "Karma," which means the law of cause and sequence; that every cause must be followed by an effect of a similar nature, that every action must produce similar reaction, and conversely every reaction or effect is the result of an action or cause of a similar character. Thus there is always a balance and harmony between cause and effect, between action and reaction. This law of Karma has now become a fundamental verity of modern science. It is called by different names: the scientists call it the law of causation, the law of compensation, the law of retribution, the law of action and reaction, but they all refer to the same idea,—that every cause must produce a similar result and every action must produce a similar reaction.

Now these ancient thinkers of India applied this law of Karma to explain the destiny of human souls, and it was upon this law they based the theory of Transmigration. They maintained that human souls are bound by this irresistible law and cannot get out of it; their thoughts and deeds are the causes which produce results of similar nature. So their future birth does not depend upon their whimsical, free choice, but it is limited by the thoughts and deeds or misdeeds of their previous lives. In the Platonic idea we find that the souls go according to their choice. They may not take a human form if they prefer an animal form, but in the Hindu idea of transmigration we find that it is not a result of free choice, but, if our thoughts and deeds force us to take a particular form, then we are subject to the law of Karma, which governs our future birth and the evolution of our souls. Consequently the Hindu theory of Transmigration differs fundamentally from the Platonic as well as from the Egyptian idea of Transmigration. In the Platonic and Egyptian theories we see that the souls, after leaving the body, enter into another body which is waiting to receive the migrating soul, but in the Hindu theory of Transmigration the body is not waiting to receive the migrating soul, but on the contrary the soul, being subject to the laws of evolution, manufactures the gross material body according to its desires and tendencies. Just as a germ of life will develop a grosser form by cellular subdivision, by growth, and by assimilation of the environmental conditions, so the germ of the human soul will manufacture the body by obeying the laws which govern the physical plane. Parents are nothing but the channels through which the migrating souls receive their material forms. Parents do not create the souls; they have no power to create. They can only give the suitable environments necessary for manufacturing a gross physical body. The souls come with their tendencies, with their desires, and they remain as germs of life.

Now these germs of life contain vital forces, sense powers, psychic powers, and ethereal particles of matter. At the time of death the soul contracts and withdraws all its powers from the sense organs to its innermost center, and in that contracted state it leaves the body. But these powers do not leave the soul. By the law of persistence of force and conservation of energy they remain latent in that center until environmental conditions become favorable for their remanifestation. Rebirth means the manifestation of the latent powers which exist in the germ of life or in the individual soul. These germs of life are called by different names. Leibnitz called them monads and modern scientists call them bioplasms or some such name, but the Vedanta philosophers describe them as subtle bodies. These germs or subtle bodies are subject to evolution and growth; they arise from lower to higher stages of development, from the mineral through the vegetable to the animal kingdom and eventually they become human beings and then they go on progressing.

In the Platonic theory the idea of progress, growth or gradual evolution of the soul from the lower to higher stages of existence is entirely excluded, because, as I have already said, the migrating substance is of a fixed quantity with fixed qualities, that is, these qualities do not change and are not affected by either growth or evolution. They are constant quantities. In order to differentiate these two ideas we should call the Hindu theory of Transmigration by the term "Reincarnation." The Hindu or Vedantic theory of Reincarnation, however, is not the same as the Buddhistic theory of Rebirth, for the Buddhists do not believe in the permanence of the soul entity. There is another point where the Reincarnation theory differs from Platonic transmigration. According to this theory of Reincarnation there is growth and evolution of each individual soul from the lower to higher stages of development. The soul or germ of life, after passing through the lower stages, comes to the human plane and gains experience and knowledge; and after coming to the human plane, it does not retrograde to animal bodies. The Platonic theory teaches that human souls migrate into animal bodies or angelic bodies and return from the angelic to the human or the animal, and that some of them prefer to become animals; while the theory of Reincarnation, taking its stand upon the scientific truth of gradual evolution, teaches that the human souls have already passed through different grades of the animal, nay, of the vegetable kingdom, by the natural process of evolution. After having once received the human organism, why should a soul choose to go back to the lesser and more imperfect organism of an animal? How is it possible for a lesser manifestation to hold a greater one? Why should a greater manifestation choose more limited forms in preference to those of others? This question arises in the Platonic theory of Transmigration. Therefore, the Reincarnation theory, or the theory of Transmigration according to the Hindus, rejects this idea of the going back of human souls to animal forms. We have already passed in the evolutionary process through the lower grade of animal organisms. Now that we have outgrown them why should we go back to them?

It is true, however, that in India there are many uneducated people among the Hindus who believe that human souls do migrate into animal bodies after death to gain experience and reap the results of their wicked deeds, being bound by the law of Karma; but in the Platonic theory the law of Karma plays no part in the transmigration of souls. The educated and thoughtful minds of India, however, accept the more rational and scientific theory of Reincarnation. Although there are passages in the scriptural writings of the Hindus which apparently refer to the retrogression of the human soul into animal nature, still such passages do not necessarily mean that the souls will be obliged to take animal bodies. They may live like animals even when they have human bodies, as we may find among us many people like cats and dogs and snakes in human form and they are often more vicious than natural cats, dogs or snakes. They are reaping their own Karma and manifesting their animal nature, though physically they look like human beings. This kind of retrogression is possible for one who after reaching the human plane goes backward on account of wicked thoughts and deeds on the animal plane. Such a temporary retrogression brings knowledge and helps it in its onward progress toward the manifestation of higher powers on the higher plane of consciousness. All the wicked thoughts and wicked deeds are nothing but the results of our own mistakes. What is sin? Sin is nothing but a mistake and it proceeds from ignorance. For instance, if I do not know that fire burns, I may put my finger into it and get burned. The result of this mistake is the burning of the finger and this has taught me once for all that fire burns; I shall never again put my finger into fire. So every mistake is a great teacher in the long run. No one is born so high and perfect as not to commit any mistake or any sin. Every mistake like this opens our eyes to the laws of the universe by bringing to us such results as we do not desire. As one life is not enough to gain experience in all the stages of evolution, we must have to admit the doctrine of the Reincarnation of the soul for the fulfillment of the ultimate purpose of earthly life. Professor Huxley says: "None but hasty thinkers will reject it on the ground of inherent absurdity. Like the doctrine of evolution itself that of transmigration has its roots in the world of reality."