Occasionalism or the doctrine of Occasional Causes, is the name of a religious philosophical theory marking an sera in the development of the philosophical doctrine as to the relation between spirit and matter, and especially between the human mind and the human body; or, perhaps better, the synchronous action of mind and body. The presupposition on which the system therefore rests is dualism, i.e. the antagonism between spirit and matter. Christianity, by means of revelation, had solved the question concerning this heathen view of antagonism, by considering matter as the medium and organ of the manifestations of the spirit. Yet in the Middle Ages the remembrance of the heathen dualistic view again got the ascendency, and scholasticism found itself unable to solve the problem of removing that antagonism. While scholastic realism had for a long time permitted the occasional and material to be absorbed as insignificant in the general notion of the mind, the renewed nominalism (q.v.; SEE OCCAM ) had used spiritual knowledge as the opponent of empiric reality, and the dualistic opposition between spirit and matter is therefore equivalent to that between realism and nominalism. Descartes, the founder of modern philosophy, followed the consequences of this dualism. According to him, the essence of mind is thought; that of matter, extension; and these two counterbalance each other. Hence the mind and the body, taken in themselves, have nothing in common. The life. of the body is a mechanical evolution, entirely distinct from the intellectual evolution of the mind. Yet the soul can modify the evolutions of the body, as God (by a positive act) has connected. it with the body, binding them together, and placing it in the pineal gland, where it is most intimately connected with the body. Descartes did not solve the problem of the manner in which the mind and the body are united. Arnold Geulinx sought to solve it after the manner of De la Forge (see Sigwart, Gesch. d. Philosophie, 2:198), by saying in his Ethica that mind and body work together through the cooperation of God. In case the will operates, God makes the body act accordingly; and in case the body is affected, God makes the mind to perceive it. Thus in the first case spontaneity, and in the second receptivity are but the reflex of divine actions; man becomes a simple spectator, for the action of his will, as well as that of his body, is a divine action. The causality is God, and therefore to be considered as absolute, "unavoidable. According to this theory, the body ceases to be the mediate cause whenever the mind assumes (though it is only in appearance) this position, and vice versa. The idea is that human receptivity and activity, proceeding sometimes from the mind, sometimes from the body, are only perceptible as divine actions. Geulinx, therefore, draws no distinction between the relative action of the creature and the absolute action of God. His system of occasionalism is consequently incorrect, as his starting-point, the occasio. is fallacious. The system cannot be properly called casulalism, but by its fatalism stands closely allied to pantheism. Malebranche tried to solve the question in a similar manner, yet in his theory the mediate causes on both sides are still more restricted. In Descartes they stand opposed to each other, connected only at one point; in Geulinx, they are alternately appearing and disappearing; in Malebranche, they really exist only in God; finally, according to Spinoza, they are two opposite human modes of representing the always identical action of the unchangeable divine substance. Yet these notions correspond to two infinite attributes of the divine nature, which always reveal themselves whole; sometimes the all-powerful body, sometimes the all- powerful mind. The opposition between mind and matter is therefore here only an apparent. opposition. Leibnitz, who objected to the occasionalist hypothesis on the ground that it supposes a perpetual action of God upon creatures, and as but a modification of the system of direct assistance, sought to carry out more fully the idea of Geulinx; his monads are all of the same nature, and each represents one and the same universe, thus producing absolute harmony; but as individuals they are all completely distinct from each other, progressing harmoniously, and thus corresponding to each other, and constituting a divinely pre-established harmony. The body and the soul are subject to different laws; but God has so regulated the parallelism of their action that it results in a harmonious whole. Thus the occasionalism of Geulinx is annulled by the theory of a regular system of causes and effects, or harmony, by virtue of which we find in each moment a double series of intermediate causes accompanying an originally combined impulse. Leibnitz perceived a real alternate action of the body and the mind, but rejected it. Sensualism, on the other hand, considers the mind as the reflex of the sensitive faculty, while idealism looks upon the sensitive faculty as the reflex of spiritual spontaneity. From this we may conclude that Descartes had not yet fully reached occasionalism, while Leibnitz had gone farther. The real medium is the system of Geulinx. — Herzog; Real-Encyklopadie, 10:522. See Ueberweg, Hist. Philos. 2:42, 54; Newell, Specul. Philos. 1:99.