The Scholastic doctrine of the soul is essen tially Aristotelian. In the form held by Saint Thomas and now the official philosophy of the Catholic Church, it consists of the following dogmas: (1) the soul, which is not divided after the fashion indicated by Aristotle, is the form of the body; (2) it is a substance, but is incomplete in the sense that it has a natural fitness for association with a body; (3) it is spiritual and without extension; (4) it is created at a definite moment in the develop ment of the organism. Of course, the scholas tics all maintained the immortality of the soul.
The modern period of philosophical thought is marked by a very important change in the notion of the soul, as has been shown. The scholastic philosophy perpetuated the Aristotel ian concept of the soul as form or entelechy. While it is true that the scholastics regarded the soul as a substance, they considered it, not as merely coequal with matter, but as the organizing factor in the soul-matter complex which constitutes man. The body was thus in a sense subordinated to the soul. On the other hand, in the philosophy of Descartes, soul and body are co-ordinated as respectively the thinking and the extended substances. As a substance is that which possesses attributes, it is quite a different sort of thing from the Aristotelian form, which gives to matter its attributes. The soul substance is of course differentiated into individual souls; but of the nature of this differentiation Descartes says little or nothing. The existence of my indi vidual soul is guaranteed to me by the famous principle, °I think, therefore I am." After the Cartesian dialectic has established the existence of God and the material universe, the next problem is the correlation of the ex periencing soul and the material objects of its experience. This correlation, which according to Descartes is guaranteed by the perfect hon esty of God, is supposed to take place in the pineal gland. The Occasionalists go beyond Descartes in that they make the correlation between the soul and the matter depend on the act of God in each particular case. The cul mination of this trend of thought is to be found in Spinoza, who maintains that mind and mat ter are not separate substances at all, but merely two among the infinite number of at tributes of the Divine Substance. Another off shoot of Occasionalism is the philosophy of Leibnitz. Instead of a dualism of mind and matter, his philosophy is a pluralism of differ ent soul-substances, which in confused per ception may give the appearance of matter. The correlation between the content of an indi vidual soul and the universe which this content represents is established through an act of God which has pre-established the harmony of the universe. Unlike the continuous divine inter vention of Occasionalism, this act was finished once for all at the creation of the universe.
The rationalistic school of the Continent, as has been shown, ended, so far as the concept of soul is concerned, just about where it began. For Descartes, the Occasionalists, and Leibnitz, the soul is essentially substance; and even for Spinoza, it is a divine attribute possessing much of the autonomy of a Cartesian sub stance. Like the rationalists, the British em piricists began with a substantial notion of the soul, but unlike the rationalists, they car ried the notion to its absurd logical conclusion and transcended it. Locke considered the soul after the fashion of Descartes, as a substance, as the substratum of ideas. He made it a blank tablet on which the ideas are impressed, but beyond this he did not characterize it.
Though he was sure that self-consciousness exists, he made no psychological investigation into its nature. Berkeley for all his incisive criticism of the Lockeian notion of substance in its application to the material world, left the notion of soul untouched. It remained for Hume to do for mind what Berkeley had done for matter and to point out the fact that intro spection alone was unable to reveal a specific soul-entity. Putting this fact side by side with the inability of the notion of a substratum to give a real explanation of anything, he came to the conclusion that the mind is neither more nor less than the sum total of its states.
Kant, who was awakened by Hume from his "dogmatic slumber," was not the least under his influence in the matter of the soul. While he most emphatically asserts that a soul ex ists, he denies that it is immediately accessible to perception. He points out, in the course of his discussion of the paralogisms of rational psychology, that the aprioristic Wolffian psy chology is based on a confusion between the subject, which must exist in some sense or other in every act of consciousness, and the simple, lasting, personal soul. The soul, qua substance, is inaccessible to us, and the entire worth of a dialectical discussion of psycho logical matters lies in the criticism to which it subjects such theories of the soul as material ism or the opinion that we have a direct in tellectual acquaintance with a permanent, per sonal ego. Thus all metaphysical proof of immortality falls to the ground, as likewise does all metaphysical disproof. The immortality of the soul, however, is established as a postulate of the pure practical reason — of the reason as applied to affairs of conduct. The existence of morality requires that there should he a progress in infinitum of the imperfect human will toward the perfection enjoined by the moral law. Kant's attitude towards the soul may be summed up in the statement that the soul can only be thought by the pure reason, but may be known by the practical reason. This ability of the practical reason to grasp matters that are partly veiled to the pure rea son is known by Kant as the primacy of the practical reason. The Kantian primacy of the practical reason is repeated in the philosophy of the romanticists under the form of volun tarism. Fichte and Schopenhauer both empha size the part played by the will in the constitu tion of the soul. The ego, which is the basis of the entire Fichtean philosophy, is grasped in a voluntary act of intellectual intuition, which exhibits to us the law of duty. The ego is immediately aware of its own free act. For Schopenhauer, as later for Bergson, the intellect is but a schematization of the will, which con stitutes the true nature of the human being as well as of the universe. Hegel agrees with the Kantian refutation of rational but regards the Kantian antinomies constituting Kant's refutation merely as a few of an indefi nite number of antinomies having their roots in Being itself. Herbart makes the soul one of his undefined primitive concepts. It is simple, absolute and transcends the bounds of space and time. Its only activity is self preservation and ideas arise when it acts to preserve itself in opposition to another real. Lotze considers that the soul and body inter act and that mind is but the higher, explicit development of what is found in the grossest matter. The philosophy of Fechner is like wise a panpsychism (q.v.) which makes the entire universe consist in a hierarchy of souls subordinated to the world-soul of God, whose body is Nature.