Although the theories of mind/brain relationship prevalent in the 19th century -- epiphenomenalism, interactionism, dual-aspect monism, and mind- stuff -- were formulated in the context of science, they, like their predecessors, were attempts to deal with the metaphysical complexities of the Cartesian impasse. It is not surprising, therefore, that these views evolved for the most part as variations on themes already addressed.
In 1870, Shadworth Holloway Hodgson (1832-1912), an English philosopher, published a two-volume work entitled The Theory of Practice . In it he provided the first modern articulation of a view that he termed epiphenomenalism. Descartes, of course, had conceived the idea that animals were purely physical automata devoid of mental states, a notion that carries with it the implication that a completely self-sufficient neural mechanism can produce complicated and apparently intelligent acts. In La Mettrie and, later, in Cabanis, this view was extended to humans, but moderated so that only the causal efficacy and not the actual existence of mental states was denied. In this regard, the French materialists anticipated Hodgson.
In The Theory of Practice [see figure 9], Hodgson argued that, regardless of their intensity, feelings have no causal efficacy whatsoever. Comparing mental states to the colors laid on the surface of a stone mosaic and neural events to the supporting stones, Hodgson asserted that just as the stones are held in place by one another and not by the colors they support, events in the nervous system form an autonomous chain independent of accompanying mental states. Mental states are present only as "epiphenomena," incapable of reflecting back to affect the nervous system.
This view was subsequently taken up, popularized, and placed within an evolutionary framework by Thomas Henry Huxley (1825-1895). In 1874, in an address in Belfast to the British Association for the Advancement of Science, Huxley presented one of the most widely cited and influential papers of the period, "On the hypothesis that animals are automata, and its history." In it Huxley suggested that states of consciousness are merely the effect of molecular changes in brain substance that has attained a prerequisite degree of organization. Animals, therefore, are "conscious automata."
In the same year, another work appeared, Principles of Mental Physiology  by William Benjamin Carpenter (1813-1885) [see figure 10], which took a position on the mind/brain relation diametrically opposed to the epiphenomenalism of Hodgson and Huxley. Carpenter was a British physician who had received his medical education at Bristol, University College London, and Edinburgh. In 1845 he assumed the Fullerian Professorship of Physiology at the Royal Institution and from 1856 to 1879 served as Registrar at the University of London. Principles of Mental Physiology contained as thoroughgoing an interactionism as the 19th century produced:
"Nothing," Carpenter wrote, "can be more certain, than that the primary form of mental activity, -- Sensational consciousness, -- is excited through physiological instrumentality. A certain Physical impression is made, for example, by the formation of a luminous image upon the Retina of the Eye ... Light excites Nerve-force, and the transmission of this Nerve-force excites the activity of that part of the Brain which is the instrument of our Visual Consciousness. Now in what way the physical change thus excited in the Sensorium is translated (so to speak) into that psychical change which we call seeing the object whose image was formed upon our Retina, we know nothing whatever; but we are equally ignorant of the way in which Light produces Chemical change ... And all we can say is, that there is just as close a succession of sequences -- as intimate a causal relation between antecedent and consequent -- in the one case, as there is in the other."
Conversely, "the like Correlation may be shown to exist between Mental states and the form of Nerve-force which calls forth Motion through the Muscular apparatus ... each kind of Mental activity, -- Sensational, Instinctive, Emotional, Ideational, and Volitional, -- may express itself in Bodily movement ... Just as a perfectly constructed Galvanic battery is inactive while the circuit is "interrupted," but becomes active the instant that the circuit is "closed," so does a Sensation, an Instinctive tendency, an Emotion, an Idea, or a Volition, which attains an intensity adequate to "close" the circuit, liberate the Nerve-force with which a certain part of the Brain ... is always charged" (pp. 12-14).
Unfortunately, in the 241 years separating Descartes' De homine from Carpenter's Principles of Mental Physiology, little progress had been made in removing the primary objection to interactionism. In the oft quoted words of John Tyndall (1871), "the passage from the physics of the brain to the corresponding facts of consciousness is unthinkable. Granted that a definite thought, and a definite molecular action in the brain occur simultaneously; we do not possess the intellectual organ, nor apparently any rudiment of the organ, which would enable us to pass, by a process of reasoning, from the one to the other" (pp. 119-120). Since this is an objection that can be just as effectively urged against epiphenomenalism, which rids itself of only half the problem of interactionism, other 19th century thinkers turned, as had their predecessors, to monism as the view of last resort. Two of the most influential monisms of the period, both aspect theories, were dual-aspect monism and mind-stuff theory.
Dual-aspect monism was the brain child of George Henry Lewes (1817- 1878). Born in London, Lewes was one of the most versatile and brilliant minds of the century. A writer, actor, biologist, philosopher, and psychologist, his interests ranged across a staggering array of topics. He was the author of a still widely read Biographical History of Philosophy (1845/1846). His Physiology of Common Life (1859/1860) converted the young Pavlov to the study of physiology, and his five-volume Problems of Life and Mind (1874/1879) constituted a major contribution to the psychology of the period.
In The Physical Basis of Mind , which forms the third volume of Problems of Life and Mind, Lewes articulated the classic modern formulation of double aspect theory, dual-aspect monism. In presenting his position, Lewes went well beyond the theories of his predecessors, supplementing the double aspect notion with a view that has come to be called neutral monism. Neutral monism involves the claim that there is only one kind of "stuff" and that mind and body differ only in the arrangement of that stuff or in the perspective from which it is apprehended.
Borrowing a metaphor from Fechner, Lewes characterized the relation of mind to body as a curve that maintains its identity as a single line even though characterized at every point by both concavity and convexity. Mental and physical processes, in other words, are simply different aspects of one and the same series of psychophysical events. When seen from the subjective point of view (e.g., when someone is thinking), the psychophysical series is mental; when seen from the objective point of view (e.g., when someone observes what is going on in the thinking person's brain), it is physical.
In the argument for the dual-aspect view, however, Lewes's innovation was by no means restricted to his neutral monism. Mental and physical descriptions, he went on to assert, employ terms which are not intertranslatable. The visual experience of a large elephant can not be adequately described through statements that characterize either the laws of light or the mechanisms of the nervous system. Mental terms, in other words, cannot in principle be replaced by physical terms. In making this claim, Lewes transferred the domain of discourse from metaphysics to language and provided what is still the best argument against extreme reductionism and the replacement of psychology by physiology.
Mind-stuff theory, which is logically akin to Lewes's dual-aspect monism, involves a number of related ideas. The first of these is that higher properties of mind, such as judgment, reasoning, volition, or the continuous flow of consciousness, are compounded from mental elements (pieces of mind-stuff) that do not in themselves manifest these higher properties. The second is that even the most basic material elements possess a small piece of mind-stuff such that when these elements are combined, mind-stuff is similarly combined. Thus, for example, when molecules come together at a level of complexity sufficient to form a brain and nervous system, correlative mind-stuff forms consciousness. And finally, in contrast to the dual-aspect monism of Lewes, which construes both mind and matter as aspects of a neutral substance, mind-stuff theory takes a position of psychical monism, arguing that mind is the only actual substance and that the material world is nothing more than an aspect under which mind is apprehended.
The idea that consciousness is compounded of mental elements which do not themselves possess consciousness was widespread during the 19th century. Thus, for example, in a passage roundly criticized by William James [see figure 11], Herbert Spencer (1870) went so far as to suggest that "there may be a single primordial element of consciousness, and the countless kinds of consciousness may be produced by the compounding of this element with itself and the recompounding of its compounds with one another in higher and higher degrees: so producing increased multiplicity, variety, and complexity" (I, p. 150). Although this idea is usually attributed to Leibniz and his doctrine of unconscious petites perceptions (see his Nouveau essais sur l'entendement humain, written in 1695 but first published in the 1765 Oeuvres philosophiques latines & françoises ), Diamond (1974) has identified a clear anticipation of this concept in the work of Leibniz's friend, Ignace Gaston Pardies (1672).
The coining of the term "mind-stuff" and the application of this view to the metaphysics of mind and body is generally credited to William Kingdon Clifford (1845-1879), who brought the components of "mind-stuff" theory together in his paper, "On the nature of things in themselves," published in 1878 in the journal Mind. The clearest and most succinct exposition of the mind-stuff position, however, was provided by Morton Prince (1854-1929) [see figure 12] in The Nature of Mind and Human Automatism (1885) Prince was born in Boston and educated at Boston Latin, Harvard College, and Harvard Medical School. Inspired by the work of Charcot and Janet on hysteria, Liébeault and Bernheim on suggestion, Gurney on the hypnotic induction of dissociation, and James on automatic writing, Prince entered early upon the study of conscious and unconscious mental phenomena which was to become his life's work. Indeed, while he was still a medical student, he won the Boylston Prize for his graduation thesis, a treatise that eventually formed the core of The Nature of Mind and Human Automatism.
In The Nature of Mind and Human Automatism, Prince concerned himself with justifying the intuitive belief that our thoughts have something to do with the production of our actions. "No amount of reasoning," he wrote, "can argue me out of the belief that I drink this water because I am thirsty" (p. 101). After rejecting parallelism as being at variance with this intuition, Prince presented the classic formulation of the mind-stuff metaphysic: "instead of there being one substance with two properties or 'aspects,' -- mind and motion, -- there is one substance, mind; and the other apparent property, motion, is only the way in which this real substance, mind, is apprehended by a second organism: only the sensations of, or effect upon, the second organism, when acted upon (ideally) by the real substance, mind" (pp. 28-29). For Prince, in other words, the psychical monism of mind-stuff constituted a modern form of immaterialism.
Like Prince, William James could never shake his conviction in the efficacy of mind; but like Hodgson, who had exerted a considerable early influence on the development of James's thought, neither could he shake his belief in the reality and efficacy of the brain. In 1890, when The Principles of Psychology was finally published, James devoted two chapters to the analysis and critique of contemporary mind/brain views, one to the automaton theory and another to the mind-stuff theory. Both chapters present extensive discussions of reasons for and against the views under analysis. The reader proceeding through the systematic dismantling of each of these views expects James, at any moment, to produce his own brilliant synthesis. Instead, however, even the redoubtable James, like many of those who had preceded him, found himself confounded by the Cartesian impasse:
"What shall we do? Many would find relief at this point in celebrating the mystery of the Unknowable and the 'awe' which we should feel at having such a principle to take final charge of our perplexities. Others would rejoice that the finite and separatist view of things with which we started had at last developed its contradictions, and was about to lead us dialectically upwards to some 'higher synthesis' in which inconsistencies cease from troubling and logic is at rest. It may be a constitutional infirmity, but I can take no comfort in such devices for making a luxury of intellectual defeat. They are but spiritual chloroform. Better live on the ragged edge, better gnaw the file forever!" (I, pp. 178-179).
James's "solution" is to opt for a provisional and pragmatic empirical parallelism of the sort to which many psychologists still subscribe. The "simplest psycho-physic formula," he writes, "and the last word of a psychology which contents itself with verifiable laws, and seeks only to be clear, and to avoid unsafe hypotheses" would appear to be a "blank unmediated correspondence, term for term, of the succession of states of consciousness with the succession of total brain processes ..." (I, p. 182). Beyond that, James suggests, we are unable to go at present without leaving the precincts of empirical science.
Wozniak, Robert H. "Mind and Body: Rene Déscartes to William James"
Bryn Mawr College, Serendip 1995
Originally published in 1992 at Bethesda, MD & Washington, DC by the National Library of Medicine and the American Psychological Association.
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