History of dualism

History of dualism

In dualism, ‘mind’ is contrasted with ‘body’, but at different times, different aspects of the mind have been the centre of attention. In the classical and mediaeval periods, it was the intellect that was thought to be most obviously resistant to a materialistic account: from Descartes on, the main stumbling block to materialist monism was supposed to be ‘consciousness’, of which phenomenal consciousness or sensation came to be considered as the paradigm instance.
The classical emphasis originates in Plato’s Phaedo. Plato believed that the true substances are not physical bodies, which are ephemeral, but the eternal Forms of which bodies are imperfect copies. These Forms not only make the world possible, they also make it intelligible, because they perform the role of universals, or what Frege called ‘concepts’. It is their connection with intelligibility that is relevant to the philosophy of mind. Because Forms are the grounds of intelligibility, they are what the intellect must grasp in the process of understanding. In Phaedo Plato presents a variety of arguments for the immortality of the soul, but the one that is relevant for our purposes is that the intellect is immaterial because Forms are immaterial and intellect must have an affinity with the Forms it apprehends (78b4–84b8). This affinity is so strong that the soul strives to leave the body in which it is imprisoned and to dwell in the realm of Forms. It may take many reincarnations before this is achieved. Plato’s dualism is not, therefore, simply a doctrine in the philosophy of mind, but an integral part of his whole metaphysics.
One problem with Plato’s dualism was that, though he speaks of the soul as imprisoned in the body, there is no clear account of what binds a particular soul to a particular body. Their difference in nature makes the union a mystery.
Aristotle did not believe in Platonic Forms, existing independently of their instances. Aristotelian forms (the capital ‘F’ has disappeared with their standing as autonomous entities) are the natures and properties of things and exist embodied in those things. This enabled Aristotle to explain the union of body and soul by saying that the soul is the form of the body. This means that a particular person’s soul is no more than his nature as a human being. Because this seems to make the soul into a property of the body, it led many interpreters, both ancient and modern, to interpret his theory as materialistic. The interpretation of Aristotle’s philosophy of mind—and, indeed, of his whole doctrine of form—remains as live an issue today as it was immediately after his death (Robinson 1983 and 1991; Nussbaum 1984; Rorty and Nussbaum, eds, 1992). Nevertheless, the text makes it clear that Aristotle believed that the intellect, though part of the soul, differs from other faculties in not having a bodily organ. His argument for this constitutes a more tightly argued case than Plato’s for the immateriality of thought and, hence, for a kind of dualism. He argued that the intellect must be immaterial because if it were material it could not receive all forms. Just as the eye, because of its particular physical nature, is sensitive to light but not to sound, and the ear to sound and not to light, so, if the intellect were in a physical organ it could be sensitive only to a restricted range of physical things; but this is not the case, for we can think about any kind of material object (De Anima III,4; 429a10–b9). As it does not have a material organ, its activity must be essentially immaterial.
It is common for modern Aristotelians, who otherwise have a high view of Aristotle’s relevance to modern philosophy, to treat this argument as being of purely historical interest, and not essential to Aristotle’s system as a whole. They emphasize that he was not a ‘Cartesian’ dualist, because the intellect is an aspect of the soul and the soul is the form of the body, not a separate substance. Kenny (1989) argues that Aristotle’s theory of mind as form gives him an account similar to Ryle (1949), for it makes the soul equivalent to the dispositions possessed by a living body. This ‘anti-Cartesian’ approach to Aristotle arguably ignores the fact that, for Aristotle, the form is the substance.
These issues might seem to be of purely historical interest. But we shall see in below, in section 4.5, that this is not so.
The identification of form and substance is a feature of Aristotle’s system that Aquinas effectively exploits in this context, identifying soul, intellect and form, and treating them as a substance. (See, for example, Aquinas (1912), Part I, questions 75 and 76.) But though the form (and, hence, the intellect with which it is identical) are the substance of the human person, they are not the person itself. Aquinas says that when one addresses prayers to a saint—other than the Blessed Virgin Mary, who is believed to retain her body in heaven and is, therefore, always a complete person—one should say, not, for example, ‘Saint Peter pray for us’, but ‘soul of Saint Peter pray for us’. The soul, though an immaterial substance, is the person only when united with its body. Without the body, those aspects of its personal memory that depend on images (which are held to be corporeal) will be lost.(See Aquinas (1912), Part I, question 89.)
The more modern versions of dualism have their origin in Descartes’ Meditations, and in the debate that was consequent upon Descartes’ theory. Descartes was asubstance dualist. He believed that there were two kinds of substance: matter, of which the essential property is that it is spatially extended; and mind, of which the essential property is that it thinks. Descartes’ conception of the relation between mind and body was quite different from that held in the Aristotelian tradition. For Aristotle, there is no exact science of matter. How matter behaves is essentially affected by the form that is in it. You cannot combine just any matter with any form—you cannot make a knife out of butter, nor a human being out of paper—so the nature of the matter is a necessary condition for the nature of the substance. But the nature of the substance does not follow from the nature of its matter alone: there is no ‘bottom up’ account of substances. Matter is a determinable made determinate by form. This was how Aristotle thought that he was able to explain the connection of soul to body: a particular soul exists as the organizing principle in a particular parcel of matter.
The belief in the relative indeterminacy of matter is one reason for Aristotle’s rejection of atomism. If matter is atomic, then it is already a collection of determinate objects in its own right, and it becomes natural to regard the properties of macroscopic substances as mere summations of the natures of the atoms.
Although, unlike most of his fashionable contemporaries and immediate successors, Descartes was not an atomist, he was, like the others, a mechanist about the properties of matter. Bodies are machines that work according to their own laws. Except where there are minds interfering with it, matter proceeds deterministically, in its own right. Where there are minds requiring to influence bodies, they must work by ‘pulling levers’ in a piece of machinery that already has its own laws of operation. This raises the question of where those ‘levers’ are in the body. Descartes opted for the pineal gland, mainly because it is not duplicated on both sides of the brain, so it is a candidate for having a unique, unifying function.
The main uncertainty that faced Descartes and his contemporaries, however, was not where interaction took place, but how two things so different as thought and extension could interact at all. This would be particularly mysterious if one had an impact view of causal interaction, as would anyone influenced by atomism, for whom the paradigm of causation is like two billiard balls cannoning off one another.
Various of Descartes’ disciples, such as Arnold Geulincx and Nicholas Malebranche, concluded that all mind-body interactions required the direct intervention of God. The appropriate states of mind and body were only the occasions for such intervention, not real causes. Now it would be convenient to think that occasionalists held that all causation was natural except for that between mind and body. In fact they generalized their conclusion and treated all causation as directly dependent on God. Why this was so, we cannot discuss here.
Descartes’ conception of a dualism of substances came under attack from the more radical empiricists, who found it difficult to attach sense to the concept of substance at all. Locke, as a moderate empiricist, accepted that there were both material and immaterial substances. Berkeley famously rejected material substance, because he rejected all existence outside the mind. In his early Notebooks, he toyed with the idea of rejecting immaterial substance, because we could have no idea of it, and reducing the self to a collection of the ‘ideas’ that constituted its contents. Finally, he decided that the self, conceived as something over and above the ideas of which it was aware, was essential for an adequate understanding of the human person. Although the self and its acts are not presented to consciousness asobjects of awareness, we are obliquely aware of them simply by dint of being active subjects. Hume rejected such claims, and proclaimed the self to be nothing more than a concatenation of its ephemeral contents.
In fact, Hume criticised the whole conception of substance for lacking in empirical content: when you search for the owner of the properties that make up a substance, you find nothing but further properties. Consequently, the mind is, he claimed, nothing but a ‘bundle’ or ‘heap’ of impressions and ideas—that is, of particular mental states or events, without an owner. This position has been labelled bundle dualism, and it is a special case of a general bundle theory of substance, according to which objects in general are just organised collections of properties. The problem for the Humean is to explain what binds the elements in the bundle together. This is an issue for any kind of substance, but for material bodies the solution seems fairly straightforward: the unity of a physical bundle is constituted by some form of causal interaction between the elements in the bundle. For the mind, mere causal connection is not enough; some further relation of co-consciousness is required. We shall see in 5.2.1 that it is problematic whether one can treat such a relation as more primitive than the notion of belonging to a subject.
One should note the following about Hume’s theory. His bundle theory is a theory about the nature of the unity of the mind. As a theory about this unity, it is not necessarily dualist. Parfit (1970, 1984) and Shoemaker (1984, ch. 2), for example, accept it as physicalists. In general, physicalists will accept it unless they wish to ascribe the unity to the brain or the organism as a whole. Before the bundle theory can be dualist one must accept property dualism, for more about which, see the next section.
A crisis in the history of dualism came, however, with the growing popularity of mechanism in science in the nineteenth century. According to the mechanist, the world is, as it would now be expressed, ‘closed under physics’. This means that everything that happens follows from and is in accord with the laws of physics. There is, therefore, no scope for interference in the physical world by the mind in the way that interactionism seems to require. According to the mechanist, the conscious mind is an epiphenomenon (a notion given general currency by T. H. Huxley 1893): that is, it is a by-product of the physical system which has no influence back on it. In this way, the facts of consciousness are acknowledged but the integrity of physical science is preserved. However, many philosophers found it implausible to claim such things as the following; the pain that I have when you hit me, the visual sensations I have when I see the ferocious lion bearing down on me or the conscious sense of understanding I have when I hear your argument—all have nothing directly to do with the way I respond. It is very largely due to the need to avoid this counterintuitiveness that we owe the concern of twentieth century philosophy to devise a plausible form of materialist monism. But, although dualism has been out of fashion in psychology since the advent of behaviourism (Watson 1913) and in philosophy since Ryle (1949), the argument is by no means over. Some distinguished neurologists, such as Sherrington (1940) and Eccles (Popper and Eccles 1977) have continued to defend dualism as the only theory that can preserve the data of consciousness. Amongst mainstream philosophers, discontent with physicalism led to a modest revival of property dualism in the last decade of the twentieth century. At least some of the reasons for this should become clear below.