SOUL, in philosophy the basis of the unity of individual consciousness and conduct. The opinions held as to the nature of this basis have naturally varied in accordance with the cur rent views as to unity and explanation. The savage, for example, can find no principle of explanation that is not at once a tangible ob ject and the bearer of human attributes, so that in his eyes the soul becomes a homunculus, a man within the man. The transition from the view of the savage to that of the uneducated man in a civilized community consists at most in the discardance of the grosser material at tributes of the soul, without the loss of any of its anthropomorphic qualities. It requires a certain degree of philosophical sophistica tion to become aware that any explanation of the soul which is to convey real knowledge must not involve the equally complicated notion of a person. The first explanations of the soul which are to be found in Greek philosophy resemble all the explanations of their period in that they make use of a material principle. This mate rial principle, which is the magnet in the philos ophy of Thales, air in that of Anaximenes, fire in that of Heraclitus and the finer atoms among the Atomists, is considered to be a moving force. Anaxagoras made the first great ad vance in the theory of the soul by isolating the notion of moving force from that of a particular material substance. The Pythagore ans adopted a view which may be regarded as an anticipation of Aristotle, in that they held the soul to be the harmony of the body. In this pre-Socratic period all the accounts of the soul place a preponderant emphasis on its cog nitive nature.
It is only with Plato that the nature of the soul comes to be the cardinal problem of philos ophy. He assigns to it a place intermediate between not-being and the realm of Ideas. The world-soul is the harmony of '
The Aristotelian view of the soul is pecul iarly interesting in that it involves motives which are active in the philosophy of the pres ent day. He places the soul definitely in that category of being corresponding to the Platonic Ideas — the realm of pure forms. The soul
is the formal cause of the human body and since the body is an organism, the soul is also the final and efficient cause. In Aristotle's own language, the soul is the entelechy of the body. Like the Platonic soul, the Aristotelian soul is tripartite. It contains a vegetative part, which superintends the functions of assimilation and propagation and constitutes the entire soul of plants; an animal soul, characterized by the powers of locomotion and sensation, which sup plements the vegetative soul throughout the animal kingdom and a rational soul, found only in man. The principle of unity connect ing these three faculities is not explained. The question of the oneness of personality is com plicated by the notion of the soul as an immate nal principle. Aristotle denies immortality to the soul, which he conceives to he created like the body in the act of begetting.
The Stoic psychology is essentially mate rialistic. The soul is nothing but fire or breath uniting the body much as the world-soul of fire unites the world. The soul consists of reason, the power of reproduction, speech and the five senses. Personal identity resides in the reason, but the individual soul is a part of the world-soul. The soul exists after death, though not for an eternity. Epicureanism took over bodily the psychological theory of atom ism. The soul, according to the Epicureans, is made up of the finest fire-like atoms, the movements of which are sensation and Immortality is completely denied. Lucretius distinguishes two levels of psychical life; the lower, animal anima, and the higher animus, presiding over emotion and cognition. The Neo-Platonists consider intelligence, soul and matter as successive emanations from the One Soul, is consequently prior to body, and more real than it. This opinion is in the philosophy of the Gnostics combined with the tripartite division of human nature characteristic of the older Platonism. In place of the desiderative part of man, according to the Platonic philos ophy, they put the body; in place of the spirited part, the soul; in place of the intellectual part, the spirit. Corresponding to the ethical and religious trend of Gnosticism, the highest place is no longer given to reason, but to that new element which enters into the human soul upon conversion. In the later Christian philosophy, the "soul') and are fused into a single entity. In Saint Augustine there are found many of the motives which characterize later medimval and modern philosophy. The body soul dualism based on the distinction between thought and extension appears in his philosophy as well as in that of Descartes. He retains the Aristotelian notion of the soul as final cause and disclaims all knowledge of the origin of the soul.