effool, licnios that thcro is any distimtinn between soul ami body. The Stoics dosrribed the .soul as a part of tlie material world-substanee; the Kpicureans lield that it is a eoinpouud of lualerial atoms; modern Materialism knows no substantial soul except the nervous system; Cabanis, for instance, proclaims his materialism in the well-known crude formula: "The brain digests impressions, and organically secretes thought." I'.syeliological materialism, as metaphysi- cal materialism, <'lo.ses its eyes to those ))henoniena of the soul which it cannot explain, or even denies that such phenomena exist. (B) Monism of the idealistic type takes an entirely ojjposite cour.se. It reduces the body to mind or mental conditions. Some of the neo-PIatonists lield that all matter is non-c.xistent, that our body is, therefore, an error on the part of our niintls, and that the soul alone is the personality.
John Scotus Eriugena, influenced by the neo- Platonists, held the body to be a resultant from incorporeal qualities which the soul, by thinking them and synthesizing them, creates into a body for itself. In modern times, Berkeley included the human body in his general denial of the reality of matter, and main- tained that there are no substances except the soul and God. The grounds for this belief are epistemo- logical. Psychological Monism runs counter to com- mon sense and experience. Historically, it is a reaction against materialism. To refute materialism it is not necessary to deny that the body is a reality. The un- reflect ing dualism of common sense and the scientific dualism which the Scholastics built on the facts of ex- perience steer a safe and consistent course between the h;isty generalization of the Materialist, who sees noth- ing but body, and the bold paradox of the Idealist, who recognizes no reality except mind.
(C) A third kind of psychological Monism goes bj' the name of psychophysical parallelism. It maintains two principles, the one neg.ative and the other affirmative. First, it denies categorically that there is, or can be, any direct causal influence of the soul on the body or of the body on the soul: our thoughts cannot produce the movements of our muscles, neither can the action of light on the retina produce in us the "thought" of a colour. Secondly, it afhrms in some shape or form that both the body and the soul are phases of something else, that this something evolves its activities along two parallel lines, the physical and the psychical, so that the thought, for instance, of moving my hand is synchro- nous with the motion of my hand, without one in any way influencing the other. This is the doctrine of Occasionalists who, like Malebranche, (q. v.), maintain that the union of the soul and body "con- sists in a mutual and natural correspondence of the thoughts of the soul with the processes of the brain, and of the emotions of the soul with the movements of the animal spirits" (Rech. de la V(5rit6, II, v). It is the doctrine of Spinoza, whose metaphysical Monism compelled him to hold that body and soul are merely aspects of the one substance, God, under the attributes extension and thought, but that they unfold their modes of activity in a manner preor- dained to correspondence (Eth., II, ii, schol.). Leibniz meets the difficulty in his own characteristic way by teaching that all monads are partly material and partly immaterial, and that among all monads and their activities there exists a pre-established harmony (see Leibniz; Monad). In the so-called Identitdtsphiloxnphie of some German Transcenden- talists, such a.s Schelling, reality is mind in so far as it is active, and matter in .so far as it is pa,ssive; mind and matter are, therefore, two harmonious, but in- dependent, series of phases of reality. Fechner's view is similar: he holds that the reality perv;iding the whole universe is at once physical and p.sychical, that the phy.sical is the "exterior" and the psychical the "interior", or "inner", side of reality, arid that
the body and ,soul in man are but one instance of a parellelism which prevails everywhere in nature. Paulsen ("Inlrod. to Phil.", tr. Thilly, 87sqq.) holds that "two propositions are contained in the theory of |)arallelism: ( I ) Physical proce.s.ses arc never cITccts of l),sychical i)roccss('s; (2) Psychical proccs.ses are never elfccts of physic'al processes," lie adopts Fechner's panpsychism, maintaining that "everything corporeal points to .something else, an inner, intelligible ele- ment, a, being for itself, which is akin to what we experience within ourselves". Both the corporeal and the "inner" are parts of the univensal .system, which is the body of God, and, though they do not interact, they act in such a way that harmony results.
Herbert Spencer uses the word paralleiism in a slightly different sense: the separate impressions of the senses and the stream of inner conscious states must be adjusted by the activity of the mind, if the two series are to be of any use to the developing or evolving animal or man; that is, there must be a parallelism between a certain physical evolution and the correlative psychical evolution" (Principles of Psych., n. 179), while both mind and matter are mere "symbols of some form of Power absolutely and forever unknown to us" (op. cit., n. 63). This idea finds favour among the evolutionists generally, and has one distinct advantage: it obviates the neces- sity of explaining many phenomena of mind which could not be accounted for by the principles of mate- rialistic evolution. Thus, under the name "double- aspect theory" it is adopted by Clifford, Bain, Lewes, and Huxley. Among empirical psychologists parallel- ism has been found satisfactory as a "working hypoth- esis". Experience, it is maintained, tells us nothing of a substantial sou! that acts on the body and is acted upon. It (loos tell us, however, that psychical states are apparently conditioned by bodily states, and that statesof bodyapparently influence statesof mind. For the purposes of science, conclude the empiricists, it is enough to maintain as an empirical formula that the two streams of activity are, so to speak, parallel, though never confluent. There is no need to ground the formula on any universal metajihysical theory, such as the pan-p.sychism of Fechner and Paulsen. It is enough that, as Wundt points out, the facts of ex- perience establish a corrcspdndcnce between physical and psychical, while the dissimilarity of the physical and the psychical precludes the possibility of one being the cause of the other. To all these parallelistic ex- planations of the relations between soul and body the Scholastic dualists take exception. First, the scho- lastics call attention to the verdict of experience. Up to a certain point, the facts of experience are capable of a parallehstic, as well as of a dualistic, explanation. But when we come to consider the unity of conscious- ness, which is a fact of experience, we find that the theory of ])arallclism breaks down, and the only ex- planation that liolds is that of dualists, who maintain the substantiality of the soul. Secondly, if the parallelistic theory be true, what, ask the Scholastic dualLsts, becomes of the freedom of the w ill and moral responsibility? If our mental and liodily states are not to be referred to an immediate personal subject, but are considered phases or aspects of a universal substance, a cosmic soul, mind-stuff', or unknown "form of Power", it is not easy to see in what sense the will can be free, and man be held responsible for his mental or bodily acts.
In a minor sense the word monism is sometimes used in psychology to designate the doctrine that there is no real distinction between the soul and its faculties. Psychological dualism holds that soul and body are distinct, though incomplete, substances. But" how about the soul itself? Plato's doctrine that it hius three parts has had verv little following in philosophv. Aristotle distiiiguishe<l between the sub- stance of the soul and its powers (oucd/icis), or faculties,