Humans are quite familiar with their experiences, their thoughts, their desires, their fears and hopes, agonies and aspirations. These are commonly referred to as mental states; and one’s possession of these states or anyone of them is evidence that one is possessed of a mind. The question, however, arises regarding the real nature of the mind, and the medium in which these mental states or processes occur. Another question relates to the possibility of post-mortem existence of the mind.  Where does the mind come from, if it is not part of the body, and where does it go from here?  A further complication worth considering concerns the status of artificial intelligence. Are purely physical systems such as computers, capable of some of the experiences listed above? Can computers think? These are the questions that this article tries to explicate in detail.



Central to the problematic of the mind is that the (concept) word ‘mind’ does not seem to have an obvious referent.  As a substantive noun ‘mind’ should designate an object; it should point to an object in the world or point to a state of affairs.  But when you try to point to its designatum you end up with a brain, which is not quite what we traditionally mean by ‘mind’.  The difficulty has been complicated by the traditional construal of the mind as some immaterial principle in the body that is responsible for self-actuation in a living thing.  Thus the mind and the soul were indistinguishable.  This conflation of mind and soul goes back to the Presocratics and was officially endorsed in Plato’s works – Meno, Phaedo, Republic, etc.  It is equally evident in Aristotle’s De Anima, as well as in Rene Descartes, as we shall see shortly.

In contemporary Western discourse the mind has come to displace the soul since the latter’s designatum has become an empty shell (as naturalist philosophers would say).  Mind now is the seat of consciousness.  The word has come to designate consciousness or the power (Aristotle’s Dunamis) of consciousness (experience, intelligence, etc.).  But consciousness is always a subject’s (somebody’s) consciousness.  It is subjective.  How does a state that is inherently subjective enjoy public criteria of reference: viz. how does the term mind become a meaningful concept for us when consciousness is inherently subjective?  That is part of the problem raised by Wittgenstein (1953) in The Philosophical Investigations and which PF Strawson (1958) tried to resolve in ‘Persons’.               


Historical background

Since Plato the idea that mind and body were two distinct entities has developed firm roots in philosophy.  In the Phaedo, for example, Plato canvassed the view that mind and body were separate because each had a distinct sphere of operation: the mind dealing with reasoning and understanding, the body dealing with our sensations and passions.  It was central to Plato’s thought that the mind could better accomplish its proper function, i.e., the quest for knowledge of truth, without the assistance of the body (Phaedo 65-6: Republic 510-11).  Indeed, for Plato, the body, far from facilitating the operations of the mind, is an obstacle frustrating the mind at every turn.  It is from these considerations that Plato regarded the body as a prison of the mind from which it seeks release (Phaedo 64; Republic 611-12).  Hence his plea to philosophers (i.e. seekers of truth) to practise death; viz., to free their minds from the distractions occasioned by the needs of the body, in order to have a successful enterprise (Phaedo 65).  Yet, despite the sharp distinction Plato drew between mind and body in the Phaedo, when he made a detailed analysis of the mind in Republic IV, he strongly promoted the idea that it was not only the exercise of our intellect but also the operation of our passions that belonged to the sphere of the mind.  According to the tripartite conception, our desires for food and drink and cravings for glory and revulsion against disgrace, all occur in the medium of the mind.  We are, none the less, reminded there that the pre-eminent faculty of the mind is reasoning.  For it is in the cultivation of the faculty of reason that our soul could attain salvation and true happiness.  The significance of Plato’s thesis in relation to the current debates of the mind is that, broadly speaking, he seemed to have entertained the widely held belief that our bodily desires, emotions and sense-experiences are realised in the mind; at the same time he seemed to be insisting that the proper function of the mind is the contemplation of the forms.  The faculty of reason, he urged, could achieve this goal, only if it parted company with the other two faculties: the appetitive and the spirited.  Clearly, for Plato, the mind is of a kind totally divorced from the nature of the body and survives the body (Phaedo 79-80), yet the mind, more often than not, carries with it to the afterlife the emotions and desires characteristic of earthly existence (Phaedrus).

In a similar vein, Aristotle in De Anima espoused a broad conception of the mind that included our bodily desires and sensations together with our emotions and quest for knowledge.  He thus regards passion, gentleness, fear, pity, confidence, joy, loving and hating as affections of the soul; but these affections, he noted, also involve the body (De An. i.1).  In support of this remark he observes that, whilst the natural scientist gives a material definition of anger (viz., as the boiling blood and hot stuff around the heart), the dialectician offers a formal definition (viz., as the desire for retaliation or something of the sort).  It would thus be improper to say that the soul pities, learns, or thinks, but to say rightly that man does these with his soul (De An. 1.4).  The moral is that man, as a composite of body and soul, is so able to carry out these activities on account of that union of body and soul.  The same applies to the faculty of sense-perception.  In De Anima III.4 Aristotle tells us that the faculty of sense-perception is not independent of the body.  Even so, he, at the same time, urges the view that all the other faculties of the mind perish with the body, with the notable exception of the active reasoning element because the intellect is distinct and unmixed with the body (de An. III.4-5).  For Aristotle, then, that part of the soul known as the active reason, or the intellect, that alone is distinct from and operates independently of the body; and it is this part that survives the destruction of the body (De An. I.4 & III.5).

There is thus clear evidence that traditionally sense-experience and emotional states have been construed as events in or states of the mind, together with the intellect.  The tension that has characterised this construal of the mind is the temptation, amongst these very thinkers who espouse this broad conception of the mind, to regard the operation of the faculty of reason, to the exclusion of the senses and the passions, as the bona fide function of the mind.  It is perhaps in an effort to rid the traditional view of this tension that Thomas Aquinas and other Christian thinkers drove a sharp wedge between the faculty of reason and the faculty of sense.  In Summa Theologica Ia.54, 5 Aquinas admonished us to ‘distinguish in the human soul between the powers that function in and through organs of the body, and which in fact therefore are activities of various parts of the body (sight of the eye, hearing of the ear, and so forth), and other powers that do not function in and through a bodily organ.  Amongst the latter powers are intelligence and will.  For Aquinas then the intellect and sense constitute the boundary between mind and body.  Accordingly, judging, willing and understanding are the functions of the mind, properly so called, in contrast to feelings of pains, joys and sorrows and experiences of touch, taste, smell, and sound, which belong to the operations of the body.  This cleavage that Aquinas sought to create did have its own problems: one of which was how to account for the moods of the angels and of the disembodied souls.  For if the angels did not have bodies then they could not share in those psychological states that are usually associated with the body (Sum. Theo. I a 77 &82).  Aquinas was thus forced to develop and elaborate theory in order to account for the joys of the good angels and the sufferings of the evil ones within the realm of their intellect or the will.

Rene Descartes was among the later thinkers who rejected the idea of splitting the powers of our psychical endowment between the body and the mind.  But he also went a step further by insisting that all so called bodily passions, insofar as they belong to the experiential, occur in the mind – in the same sense as the operations of our intellect and will are said to occur in the mind.  Thus in the opening lines of Meditation III he reiterates the one proposition that survives his dubito argument: ‘I am a thing which thinks, that is to say, which doubts, affirms, denies, knows a few things, is ignorant of many, which loves, hates, wills, does not will, which also imagines, and which perceives.’  For the sceptic, who might think that the modes of thought outlined here do not include sensations of pain and pleasure, should be reminded of the reply Descartes sent to his contemporary, Mersenne, who accused him of having a narrow construal of thought.  In his letter to Mersenne (cited by Anthony Kenny) Descartes explains: ‘for willing, understanding, imagining, and feeling are simply different ways of thinking, which all belong to the soul.’  There is sufficient textual evidence to the effect that Descartes consistently construed thought to embrace all forms of mental experience.  This is clearly borne out in Meditation II where he first attempted to define the first person.  He made clear there that thinking embraced doubting, perceiving, affirming, denying, willing, imagining, and feeling.  So in Meditation VI when discussing the relationship between mind and body he reminds us once again that the faculties of feeling and perceiving are within the mind.  In short, for Descartes mental experience covers both sensory experience as much as it includes reasoning, understanding and imagination.

Of interest to our discussion is the nature of the relationship that Descartes sought to draw between mind and body.  To be sure, Descartes inherited from his predecessors the doctrine that soul and body were two distinct entities.  His aim then was not to challenge the dual nature of man but to reinforce the arguments for the dualist thesis. 


As a matter of fact, the notion of dualism which have been using so far, and espoused by Descartes, is known as ‘substance dualism’.  This is the doctrine that the universe is composed of two distinct kinds of substances:  the universe is composed of two distinct kinds of substances:  the spiritual substance and the material substance.  A distinguishing feature of Cartesian dualism is that ontologically both mind and matter have equal status.  Furthermore, it is part of this thesis that, as a matter of fact, spirit and matter interacts even though that interaction is not necessary and so remains a mystery.

A less radical version of dualism is dubbed property dualism’.  As the name suggests, this doctrine concedes that the universe is composed of one fundamental entity, and that this entity possesses two distinct kinds of properties, one being physical and the other being mental.  This idea is founded on the observation that the mind has a special set of properties possessed by no other kind of physical object.  Our beliefs, thoughts, sense-experiences, desires and emotions, etc, are held by this theory to constitute the special properties of the mental that are non-physical.  This claim invites the questions, what constitutes a physical property? Descartes suggests that geometrical properties like: extension, volume, shape and size are the best examples of physical properties.  But modern day physical theorists, while accepting that these are, indeed, physical properties, would urge that they are perhaps not the most crucial qualities of matter.


The above suggests Descartes’ arguments in support of dualism, which were, in the main, three: 1) the argument from dubito, 2) the epistemological argument, and 3) the incompatibility of mental and physical properties.

Descartes intended to use the dubito argument to flesh out unassailable truths that would serve as the foundation of our understanding of the universe.  Thus he says in Discourse IV, ‘... as I wanted to concentrate solely on the search for truth.  I thought I ought to ... reject as being absolutely false everything in which I could suppose the slightest reason for doubt, in order to see if there did not remain after that anything in my belief which was entirely indubitable.  Accordingly Descartes rejects as false the ideas occasioned by sense perception, our theories of mathematics and science, and belief in god.  In short, consistent with his journey on the sceptical road, he subjects to doubt all the commonly held beliefs – including the belief that he who doubts has a body.  The outcome of the sceptical argument is one indubitable truth, namely, that ‘I who thought thus must be something ...’ as doubting presupposes thinking, Descartes felt that he had discovered a basic truth in the proposition, ‘I think, therefore I am.’  This proposition, he believed, could constitute the first principle of his philosophy.  It is arguable whether you could truly deduce the existence of a person from an event, viz. thinking.  But going along with Descartes for the present, our concern is to determine all the attributes that could be justifiably conferred on the thinking thing.  It is first established that ‘I was a substance, of which the whole essence or nature consists in thinking, and which, in order to exist, needs no place and depends on no material thing.’  As noted early on, for Descartes, thinking embraced every kind of sensory experience as well as reasoning and imagination.  Thus the essence of the person is the mind: in his own words, ‘... this “I”, that is to say, the mind, by which I am what I am, is entirely distinct from the body, and even that it is easier to know than the body, and moreover, if the body were not, it would not cease to be all that it is.  Going by the sceptical procedure, Descartes can doubt that he has a body but cannot doubt that he exist: for doubting his existence would render his doubting an impossibility.  It follows that the body is not essential to his nature as a thinking thing. (Osei, 2006: 10-14). There is, however, a problem about sensory experience.  Descartes elsewhere concedes that, though perceptual knowledge is a mental state, it is difficult to conceive how perception could occur without the body.

A second claim of Descartes, as shown in the above quotation, is that it is easier to know one’s conscious state than to know that one has a body.  It has been observed that Descartes’ crucial legacy to philosophy is the claim that knowledge of the self, as a conscious being, is epistemologically prior to knowledge of the external world.  The argument underpinning this claim is that it can be more certain of my internal experiences than to suppose that these experiences are related to objects (including my body) that lie outside of these experiences.  It is plain that this argument is a corollary of the skeptical argument.  For it still a logical possibility that I might be under the illusion that I am seeing a wax, when in fact there is not wax.  But this misperception does not vitiate the fact that I am having a mental experience.  This explains why knowledge of my mental (i.e., internal) episodes informs than knowledge of external events and objects.


It seems to follow than that I have direct and certain knowledge about my internal experience; in contrast, I do not have such a direct episteme assess to the world external to my experience; this epistemological divide between internal and external entities (Malcolm 1971, p.5).


The third Cartesian argument crucial for the sustenance of dualism is the alleged incompatibility of mental and physical properties.  Descartes thought that the fundamental difference between mind and body, by in the fact that we conceive mind as a thinking and non-external thing and body as an extended non-thinking thing.  Other way properties of matter outlined in Meditation II include location, figure, and spatial movement.  These properties in addition to extension are held to be exclusive to matter.  One property arising from the extended nature of matter which, Descartes believed, sets mind apart most distinctly, is that matter is divisible.  In contrast we are told that there is unity in consciousness.  To this (divisibility of matter) might be added the age old belief that matter is inert, i.e., it is not capable of self-motion.  In Meditation II Descartes observes, ‘For as to having in itself the power to move, to feel and to think, I did not believe in anyway, that these advantages might be attributed to corporeal nature (p.104).  It may well be that matter as such is not capable of sensation or capable of thought, but we are now pretty certain that matter in not inert.  In reality each a time unit of matter contains within it a huge reserve of quantifiable active force-as the hydrogen atom clearly demonstrates.


There are, however, three properties that Descartes recognises mind shares with matter, namely: substance, duration and number.  Substance, following Aristotle, means just anything that is capable of independent existence.  And, if Descartes’ analysis of mind as correct than consciousness could exist independently of the body.  So there is no rational ground for denying the status of substance to mind.  Again, as experiences occur in time, or subsist through time, the mental is clearly situated in time.  Finally, since we have different kinds of experiences at different times, it is recognised that there are countable (i.e. numerable) mental episodes (Meditations III, 122-3).




The dualist thesis


The Mentalist (Idealist) thesis

One line of approach that has sprung from the Cartesian tradition is the theory that there is one basic entity and that entity is wholly mental: this is the doctrine of mentalistic realism canvassed by contemporary non-materialist philosophers, such as, John Foster and TLS Sprigge.


Berkeleian Idealism

Historically George Berkeley has been credited with the best and most consistent argument for the case of idealism. It will thus be instructive to start from him.

Berkeley, in writing The Principles of Human Knowledge, it is generally recognised, was inspired by two main motives: 1) to demolish the Lockean theory of causal realism, which offered a mechanistic account for the popular belief in external physical reality, and 2) to espouse the doctrine that it only ideas and the spirits that have these ideas, that are the true constituents of the universe. Accordingly, the first part of Principles consists of a critique of John Locke’s causal theory of matter. Thus Berkeley writes:

‘But, though it were possible that solid, figured, moveable substances may exist without the mind, corresponding to the ideas we have of bodies, yet how is it possible for us to know this? Either we must know it by Sense or by Reason. As for our senses, by them we have the knowledge only of our sensations, ideas, or those things that are immediately perceived by sense, call them what you will: but they do not inform us that things exist without the mind, or unperceived, like to those which are perceived. This the Materialists themselves acknowledge. It remains therefore that if we have any knowledge at all of external things, it must be by Reason inferring their existence from what is immediately perceived by sense. But what reason can induce us to believe the existence of bodies without the mind, from what we perceive, since the very patrons of matter themselves do not pretend there is any necessaryconnection betwixt them and our ideas? I say it is granted on all hands (and what happens in dreams, frenzies, and the like, puts it beyond dispute) that it is possible we might be affected with all the ideas we have now, though there were no bodies existing without resembling them. Hence, it is evident the supposition of external bodies is not necessary for the producing our ideas; since it is granted they are produced sometimes, and might possibly be produced always in the same order we see them in at present, without their concurrence’ (Principles XVIII)

That there exist only minds and their ideas has earlier been asserted emphatically in Principles III. In his words: ‘as to what is said of the absolute existence of unthinking thigs without any relation to their being perceived, that is to me perfectly unintelligible. Their esseis percipi, nor is it possible they should have any existence out of the minds or thinking things which perceive them.’ Clearly, for Berkeley, there is no question about the nature of the mind. Since the mind cannot be the idea it has to be the substance in which mental events and states as well as ideas inhere. The mind is therefore pre-eminently an immaterial substance.           




Summary of Forms of Idealism

We are now in a position to state three forms of idealist thesis that have emerged from our discussion of Berkeley and Hume.

  1. The world is wholly constituted of mind (a non-physical active substance, also called ‘the self’) and its ideas (commonly construed as physical objects); this mind figures in experience as perception and thought, and the ideas as the objects of perception and thought. (This is Berkeley’s thesis)
  2. The world is wholly constituted of a sequence, or collections, of sense-impressions and ideas; thus our thoughts, intentions, desires and volitions are all forms of ideas. (This is Humean empiricism)
  3. The world is wholly constituted of sheer mental processes like perceiving, imaging, willing, thinking, etc.; each mental process is rendered determinate by its distinctive property or set of properties, but these properties (like all qualities) qualify the relevant process essentially and have no being outside the process. (This is ‘pure process idealism’ akin to Humean empiricism)


In Berkeley the fundamental postulate is the self:it is the subject of sense-experience and the originator of thought and the operation of the will. Accordingly, the objects of sense-experience and thought, their qualities and relations, exists in the self. This self, as the seat of volition, has causal power. Hume, for his part, denies the notion of the self altogether and with it the concept of causal agency in Berkeley. In his view, the constraints of empiricism forbid him from entertaining such notions because they do not figure directly in sense-experience and they cannot be deduced either from it. Again, though Hume seems to recognise that the notion of mental act has some utility in his system, he did not accord it the same status as he endowed impressions and ideas.

Finally, what makes these different positions all forms of idealism is their commitment to the view that what exists must either be definable by reference to what we are aware of in perception or introspection or be capable of being constructed from these by the exercise of our imagination and reason. Consequently, the physical world, for idealism, is something that exists in the mind, as objects of perception: its being is its being perceived. This contrasts with physical realism (or, in a word, physicalism) which takes the physical world to be logically independent of the human mind and metaphysically fundamental. Thus idealism, in essence, adopts a reductionist view with respect to the physical world. This is the same as saying that, though physical concepts are meaningful in their own right, what these concepts refer to exist in experience or are the logical constructions from experience. This distinction between idealism and physicalism is going to play a crucial role in our discussion of the mind-body problem.




The Mind-Body Problem


The nub of the mind-body problem could be described roughly thus: We are aware of some intrinsic properties of the mental; We are not aware o the intrinsic properties of the physical; This gap in our knowledge is the cause of our bafflement in our attempts to account for the relationship between the mental and the physical; This bafflement, notwithstanding, a common cord that runs through mainstream dualism and physicalism is a strong intuition that the mental and the physical are causally related. The question that arises is this: Given that our knowledge of reality is incomplete, for what reasons and on what evidence must we be persuaded by one theory rather than another as offering the best account of reality?  It is in this perspective that I will try to show below that a version of materialism offers us perhaps the most coherent explanation of the relationship of the mental and the physical.


There is the need here to clarify two terminologies, namely, ‘physicalism’ and ‘materialism’, vis-à-vis Feigl and Maxwell’s treatment of the physical.  Historically ‘physicalism’ and materialism’ have been used indifferently to refer to a conceptual system that describes reality in terms of the principles and laws of physics (Armstrong 1968).  As a metaphysical theory physicalism (materialism) assists that the fundamental stuff of nature is constituted of physical properties.  Specifically, ‘physicalism’ in its classical sense is the theory that there is one fundamental reality, and that this reality is what the theory, principles and laws of physicals are all about.  This reality, physicalism holds, occupies space-time and is constituted ultimately by: the properties and relations, actions and interactions of particles, fields and energies-that is, the basic entities that physics treats.  Physicalism thus holds that all entities, properties, relations and facts are those which figure in the framework of theoretical physics and other related sciences.  Thus given physicalism, if there are entities such as phenomenal qualities of experience then these qualities ought to be captured in terms and concepts of physics.  Materialism is construed as the theory that asserts that all entities, properties, relations and events (including experience and phenomenal qualities of experience) that figure in the spatio-temporal realm are constituted of material principles and the laws that govern those principles.  Thus materialism, in its broad construal, encapsulates mental and physical predicates. It asserts that all events describable in mentalistic terms as well as those describable in physicalistic terms are both material events.  Materialism can be taken as a broader concept, as Lockwood explains, ‘because there may be more to matter than can be captured in the language of physics, more than any description couched purely in the language of physics is capable of conveying (Lockwood 1989.20).


Mentalism and the Mind-Body Problem

To round off this discussion we should consider whether any coherent idealist theory can deliver a plausible solution to the mind/body problem. Now the version of idealism, that we have discussed at length and, which reflects the broad views of Berkeley and Sprigge is a mentalist doctrine. Mentalism asserts that ultimate reality is wholly mental, that is, the mental is ontologically primitive and/or logically basic. That is to say, ultimate reality is confined to a framework of time, minds and mind-governing laws. Now, the possibility that the physical realm, while ontologically and factually derivate, is conceptually autonomous, so that physical statements cannot, without loss of meaning, be reformulated in non-physical terms. It leaves open the possibility that physical facts, though logically sustained by non-physical facts cannot adequately be expressed except by means of an explicitly physical vocabulary and an ‘immaterial-spirit substance’, or immaterial stuff; but the question of whether this stuff is itself intrinsically and wholly mental in nature is left obscure. In the Cartesian tradition, we have, on the one hand, non-self-subsistent ideas or experiences. These ideas are conceived of as dependent on minds, which, on the other hand, are ontically distinct from ideas, these minds can presumably continue to exist when there are no ideas or experiences occurring. But the paradigm cases of mental goings-on in the classical debate are just occurrent mentally contentful processes, a stream of ideas, of experiences: thought, willings deciding, dreaming, etc. It is our experience of these intrinsically mentally contenful things that gives positive content to our ideas of what the mental is. So if we suppose that there is any other kind of mental thing, namely, immaterial stuff, we have to grant that there is a sense in which we know nothing about its nature, apart from the fact that it is, somehow, the source or ground or basis of the familiar occurrent mental goings-on.

The alternative to the classical view is to construe the mind as identical with (ontically indistinguishable from) the stream of ideas themselves. But even in the case of ‘pure process idealism’ or strict idealism, which might be associated with Hume, it is left unclear whether the stream of consciousness is itself some stuff or that it is a pure process, which by definition would be insubstantial. Besides the problem of determining what we are to take the substantiality of the mind to be in pure process idealism, that a person or a mind can exist even if there is presently no mental activity going on. And if a mind is nothing other than its ideas, then pure process idealism will have to contend with as many minds as there are ideas or for the theory. The other option open to it is to construe the mind as the unifying principle of the ideas, the bond that connects one strand of ideas to other strands and thus delivers a coherent pattern of experience. But the question that comes back to haunt the theory is whether this unifying principle is itself an idea of which we are distinctly aware, or not. And the answer would have to be in the negative because this putatively unifying principle is not self manifest. Accordingly, pure process idealism is constrained to concede the unpalatable: that there are as many minds as there are ideas (in a manner of speaking).

Suppose there is a mentalist theory that is able to give a positive account of the nature of the mind and its relationship with its ideas, and thereby able to deliver a coherent account of the concept of mental. The question arises whether such a coherent mentalist theory would be interestingly distinct from a materialist theory. For from the idealist perspective the objection is ground of experiential or conscious mental occurrences. The force of this objection is that we have no real idea of how matter, as we ordinarily conceive it in physics, can be the basis of, or realise, or be, experience. But this objection is valid only if we concede the dubious assumption that the nature of the material stuff is well known, or that current physics has been able to deliver the essential property of matter. For all we know matter may very well have properties of which we have no idea; properties that might, in truth, be the basis of, or realise, or constitute, experiential occurrences. The danger for the mentalist theory is that, short of subscribing to pure process idealism with all its attendant problems, it is itself incapable of giving any positive account of the essential property of the mind. But in postulating a mind whose essential nature is unknown the theory becomes vulnerable to the materialist challenge that it has no good reason to suppose that the essential nature of the mind might not be matter after all. Thus mentalism is either internally incoherent, if it reckons that the mind is ontically distinct from its ideas, or postulate as many minds as there are ideas.

Now, we should remind ourselves that the motivation for a mentalist thesis is generally driven by the quest for a coherent account of the mind that would effectively resolve the mind/body problem. Mentalism, we would recall, is the thesis that all entities are wholly mental. There is therefore no other entity and so there is no body. But if there is no body, then, there is no mind/body problem. The conclusion is as trivially obvious as any proposition can be, granted that there is no matter. So far as our brief study of the idealist theories shows, the proposition that there exists extra-mental material thing has not been refuted. Matter is as deeply anchored in experiences as are mental properties. It will therefore be counterintuitive to reduce one to the other. In short, in an effort to reduce material properties to components of experience, and thus construe them as mental entities, idealists wish to succeed where the physicalists failed. It is our conviction that the mentalists in their effort to achieve their aim are confronted with no less difficulties as the physicalists. The mind/body problem cannot be wished away by decreeing matter out of the universe or reducing it to a mere component, a baggage, of experience. 


The Materialist theses:


Scientific/methodological Behaviourism

Behaviourism, as a philosophical theory of the mind sprang from psychology. Behaviourism in psychology is a method for studying human beings. The motivation for the postulation of a causal analysis of the mind sprang from behaviourism. For instance, B.F. Skinner, the well known American psychologist, canvassed the view that the mind is a thing, be it a material thing or a spiritual thing. It asserts that a ‘mental’ description of Socrates is not a description of what some substantive part of a Socrates- his mind-is like. Rather, such descriptions tell us of Socrates’ behaviour. Thus a behaviourist, such as Skinner, believed that they could attempt to predict and control human behaviour through the study of its environmental causes. On this view, the mind is not a thing related to the body; the relation of mind to the body is the relation of activity to agent. Mental terms get their meaning by reference to behaviour and its causes.

Behaviourists thus tend to be sceptical about the reality of consciousness. This attitude shows itself in the manner they account for bodily sensations (pain, itches, etc.), visual experiences and intelligence. Pains, as for afterimages, are not regarded as mental objects in their own right. Rather, these are construed as bodily reactions (responses) to stimuli. The person is not so much in pain as that she is exhibiting typical pain-behaviour; similarly she is not so much experiencing an afterimage, as that she is behaving in a way typical of people who are experiencing an afterimage. In both cases the behaviour constitutes the occurrence of the mental event. Since mental objects have no place in behaviourism, descriptions of humans referring to pains and afterimages are not relational descriptions linking us to pains and afterimages: on the contrary, these are complex descriptions of our physical conditions- they refer to bodily events or processes, rather than relating one object to another. This account is applied to all mental states, events, including thoughts, emotions, and intellect- the class of mental entities that are commonly taken as inner, non-physical objects. Thus to say, for example, that a person is intelligent is to say, among others, that she has a higher success rate in solving abstract and practical problems and that solutions come to her quicker and with less effort than the average person. In short, what it means to possess a mind is to exhibit appropriate responses to stimuli. There is no inner state that mentalist terms refer to other than bodily events or behaviour.


Logical Behaviourism

Logical behaviourism is, in a sense, an advanced form of scientific behaviourism. For logical behaviourism as it deals with the concept of dispositional properties. But perhaps the main distinction between the two forms of behaviourism view their theory pre-eminently as a methodological thesis for understanding human behaviour, logical behaviourists are primarily concerned with determining the status of mental concepts in our public language. Thus logical behaviourism is a linguistic thesis that tries to explicate, how it is possible for sentences that contain mental terms like: ‘thought’, ‘belief’, ‘perception’, ‘image’ or ‘memory’, to be translated into sentences about publicly observable behaviour.

Logical behaviourism is a reductionist thesis at the level of concept or language. This form of reductionism is stronger than ontological reductionism, because conceptual reduction implies ontological reduction but is not implied by ontological reduction. Thus logical behaviourism is not only claiming that mental events, like perceiving, thinking, believing, suffering, enjoying, etc., refer to behaving or else having a certain disposition to behave, but is further claiming that mental concepts have no distinctive meaning independently of the terms which we use in describing behaviour. Thus the question whether a person is intelligent or not can be decomposed into the question whether a person can solve differential equations with ease, or can understand a joke better than the average person, etc. on this showing ‘intelligent’ becomes a blanket term for a range of publicly observable performances that endow it with meaning.

Besides, behaviourism, as remarked earlier, does not recognise an inner state that grounds the dispositions they employ to explain the triggering of human behaviour. Ryle, for instance, would say that attributing a certain conditional sentences are true of her (e.g., if you sit on a needle then youwill shout in pain). There is no reference here to the inner ground of the disposition. Thus mental descriptions derive their meaning by reference to what a person does or can do. For it is a dogma of logical behaviourism that for any term be meaningful there must be a public criterion for confirming or disconfirming its referent. Accordingly, if mental terms have meaningful content they must advert to facts or events that are publicly verifiable. Furthermore, for behaviourism, since there are no public criteria upon which the alleged inner states have no meaning. The upshot is that all meaningful mental descriptions can be reduced to descriptions of psychological behaviour, that is, publicly observable fact/event.

Behaviourism has two enviable advantages over its rival theories: first, it demystifies the meaning of the term, mind; second, it dissolves ‘the problem of other minds’. In the first instance, the theory stipulates that mind does not lie behind behaviour, like some causal agent to an event (a ghost in the machine); rather, the mind is in the behaviour. It attacks common opinion for referring to behaviour as the manifestation of the mental state. Common option is mistaken in supposing that there are such ontically distinct ‘inner’ entities as mental events, processes, or states that play a causal role in producing behaviour. The postulation of inner states, the behaviourists contends has no basis in reality because they are not observable or verifiable: for the only observable referents of mental concepts is just the behaviour. But behaviour cannot be a cause of itself:for nothing is a cause of itself. So a mental event, qua behaviour, cannot be a cause itself. Hence a causal analysis of the mental is false. Moreover, in conformity with the conditions under which all words derive their meaning, there ought to be public criteria from which mental descriptions obtain, then, so claim the behaviourists, they do not, and cannot, refer to private events but to tendencies for there to be public and physical events. In the second instance, if mental descriptions do not advert to events that are antecedent to behaviour or descriptions to behave, but just the descriptions of the behaviour, or behavioural patterns-the kind of events or processes that occur in the public domain- then mental episodes are as publicly observable as are other physical episodes. Hence the problem of other minds vanishes once it is recognised that mental episodes belong to the public domain.     

Before we show what a version of materialism offers us and the physical; let us, for the moment, cast a critical glimpse at the theory of supervenience and its tendency towards physicalism.



The Theory of Supervenience

In the philosophy of mind the theory of supervenience has been involved to articulate a broadly physicalist position, or a naturalist interpretation of the mind, without the commitment to the reduction of mental phenomena to the basic entities recognizable in physics.  That is, in contrast to the claim of some mainstream identity theorist that every mental state is identical with some brain state, supervenience theorists hold that mental states are, at lease, logically antonomous of brains states.  There are two non-reductive materialist theories that give some recognition to the logical independence and effects: they are ‘supervenience’ and ‘epiphenomenalism’.  These theories acknowledge thought, the ontological dependence of conscious states on brain states and a causal connection between brain states and mental (conscious) states.  Yet, at the same time, they (more precisely: some supervenience theorists and the epiphenominalists) recognise that the phenomenology of the mental state is not reducible to its putative cause or effects.  The theory of supervenience explicates the relationship between mind and body.


The supervenience thesis in its materialist formulation was first introduced into the philosophy of mind by Donald Davidson in his articles, ‘Mental Events’ (1970).


He wrote:

Although the position I describe denies there are psychophysical laws, it is consistent with the view that mental characteristics are in some sense dependent, or supervenient, on physical characteristics.  Such supervenience might be taken to mean that there cannot be two events exactly alike in all physical respects but differing in some mental respect, or that an object cannot after in some mental respect without altering in some physical respect.  Dependence or supervenience of this mind does not entail reducibility through law or definition.


Two remarks about Davidson’s thesis are in order.  First, Davidson is firmly rejecting the identity or nomic equivalence of mental properties with physical properties.  That is to say, a broadly materialist view of the mind should not require the ‘reducibility’ of mental properties to physical properties in order to account for the inter-level match between mental descriptions vis-à-vis physical descriptions.  The notion of reducibility at play here is just as it is typically applied in explaining macro physical properties, like heat, in terms of their physical basic entities, live molecular kinetic energy.  The reduction of heat to molecular kinetic energy involves outright identities between higher-order property type and lower-order property type.  The inter-level dependency relations, that obtain between the macro and micro principles and laws is posited by physics.  There is a purely physical explanation of how heat is generated by the micro theoretical entities posited by physics are held to be coherent within the magnitudes of physics.  On this view the identity between heat and molecular kinetic energy does not only exemplify a nomic relation, because it is possible to vie a complete descriptive account of heat in micro physical seems without a remainder.  This contrasts with putative inter-level relations that G.E. Moore believes to hold between moral descriptions and physical descriptions.  In the latter case a purely physical descriptions is thought not to capture the relevant moral property that supervenes on it: the reason from Moore’s perspective is that moral properties and facts are not natural properties.  For instance, Moore thinks that a proposition of the form “Anything that possesses the natural property N (say, the inclination to bring succor to one in distress) is to possess the property of intrinsic goodness’ expresses synthetic necessary truth.  However, this synthetic necessary connection instantiated by the proposition is metaphysically rock bottom in that it is not explainable by any other facts.  J.L. Mackie’s remarks illustrate the peculiar nature o Moorean necessitation connection between natural and moral facts.  He writes:


 What is the connection between the natural fact that an action is a piece of deliberate cruelty – say causing pain just for fun – and the moral fact that it is wrong?  It cannot be entailment, a logical or semantic necessity.  Yet it is not merely that the two features occur together.  The wrongness must somehow be ‘consequential’ or ‘supervenient’:  It is wrong because it is a piece of deliberate cruelty.  But just what in the world is dignified by this ‘because’? (Mackie 1977:44).


Thus the supervenience relation that is held to obtain between physical facts and moral facts is not of the order of logical entailment such that it warrants the deduction of moral facts from an account of physical facts, and vice versa.  Now, if Davidson is following Moore in designating the inter-level relation between mental properties and physical properties as a relation of supervenience for the reason that the nature of the tie between the physical and metal phenomena is not susceptible to the sort of reductionist explanation that is intelligible in the framework of a physical theory, then materialists who are attracted to Davidson’s view are faced with the problem of given an account of supervenience that is intelligible in some materialist terms – in terms that does not render the connection between the two kinds of phenomena mysterious. 

Second, Davidson is evidently committed to the view that a broadly respectable materialist theory need only claim that physical facts and physical properties are the ontically basic ones.  We have thus a dependency relation of mental phenomena on the basic physical facts.  Now if physical properties and physical facts are metaphysically all that there are, and yet mental properties and mental facts are not reducible5 to the physical basic facts, then we are faced with the problem of placing mental properties in the realm of physical things.  Davidson construes mental properties as higher-order properties that supervene upon the physical properties.  What we should like to determine is whether a relation of supervenience can offer a satisfactory explication of the tie between mind and matter.


Since Davidson’s seminal paper on supervenience, other materialistically inclined philosophers have developed the thesis further in efforts to deal with potential objections arising from the problem sketched above.  Amongst those who have devoted much thought to the theory and have taken head on the difficulties associated with it are Terence Horgan and Jaegwon Kim(Horgan 1978;1984;1993; Kim 1978;1984).  Of interest to our discussion is the determination of the potential contribution of supervenience toward a plausible materialist theory of the mind.  To assist out assessment of the theory, let us restate the supervenience thesis in its materialist form.  Supervenience proceeds from the following claims.

It is impossible for two events (objects, states) to be identical in all their physical characteristics and to differ in their mental characteristics.  Two systems cannot differ in their mental characteristics without differing in their physical characteristics.


As we saw from Davidson’s formulation of the thesis, supervenience is a dependency relation of mental states (event, properties) on physical states (event, properties).  From the materialist point of view, the facts of physics synchronically fix, or determine, all the facts.  This sentiment is neatly captured in Terence Horgan’s succinct formulation:


Any two physically possible worlds that are exactly alike physically are also exactly alike in all other respects(Horgan 1994:239).

The metaphysical commitment of physicalism ensures that the basic constituents of the universe are physical properties (states, events).  It follows from this commitment that any other property, state or object that exists must be realised in some physical property, state or event.  Accordingly, if there are mental states – states that are themselves not describable in physicalist language terms – then, these mental states will require the presence of a physical state (or a combination of some physical states) as a precondition for their existence. However, the thesis in its present form does not mirror the ontological dependency of the mental (and other nonphysical higher–order properties) on the physical presupposed in the theory of psychophysical supervenience. For it is consistent with the thesis that any two mentally possible worlds that are exactly alike mentally are also exactly alike physically. The physical can ground the mental and the mental, it would seem, can equally ground the physical (Miller 1990:696). But this is contrary to the metaphysical commitment of materialism according to which the basic constituents of the universe are material properties. There are thus many assumptions on which the supervenience thesis is riding. Horgan, has catalogued these assumptions as inter-level constraints required to guarantee materialist metaphysics. They are as follows.


  1. Compatibility with the causal explanatory adequacy of physics. Metaphysical naturalism includes the view that physics is causally and explanatorily complete, within its own domain; i.e., every fact or phenomenon describable in the language of physics is fully explainable (to the extent that it is explainable at all) entirely on the basis of facts and laws of physics itself.
  2. Physical supervenience. Metaphysical naturalism also includes the view that the facts of physics synchronically fix, or determine all the facts.
  3. Existence of physical causal mechanism. This constraints concerns causal explanations that cite properties from higher-level theories or explanatory frameworks.  For any casual transaction where some higher level property F is cited as casually explaining the effect, there must be an underlying mechanism in virtue of which the transaction occurs – a mechanism involving a physical property (or a complex of physical properties) which, on the given occasion, physically realizes the property F.
  4. Noncoincidentality of higher-level generalizations. In order for higher-level counterfactual relation patterns to have genuine causal/explanatory relevance to phenomena that exhibit higher-level properties, the higher-level generalizations that systematize those patterns must themselves be nonaccidental (Miller 1990:238-240).

The first constraint throws up one of the key planks of physicalism: namely, the causal completeness of physics. According to it their physical antecedents in accordance with physical laws fix the chances of physical consequences. This means that if two systems are alike in all their physical characteristics: viz, share the same number of elemental properties and structure, then, they must have similar physical consequences. But that is not all. For implicit in the thesis is a commitment to a physicalist ontology according to which physical categories by themselves always suffice to fix the chances of all consequences without the help of nonphysical categories. It follows that any putative event (state or property), be it physical, mental, or what have you, that is deemed to arise from a physical antecedent must be physical in the sense that it must conform to the laws of physics.  Suppose we have two physical systems, A and B, that are alike in both physical composition and structure, and A possesses a mental property F, then of necessity B possesses mental property F. Thus on the assumption that mental events supervene upon physical events, we would not need to look beyond the realm of the physical in order to identify a set of antecedents that determines the chances of the subsequent mental events.  Therefore, a commitment to physical ontology precludes a postulation of mental categories that do not conform to the laws of physics.  But a property (state, event) that is constrained by the laws of physics is by definition a physical entity.

Many philosophers who subscribe to psychophysical supervenience generally construe the supervenience relation as exemplifying a metaphysical necessity rather than a conceptual necessity, in the sense of these terms that Kripke has made familiar.  These theorists thus hold that the psychophysical supervenience relation that obtains is sustained by the laws of nature, and that there is a metaphysical necessity about the determination relation between the mental and the physical domains.  Therefore, just as there are no possible worlds in which water is not H2O, there are not possible worlds in which ‘C-fibre’ activity is not associated with the feeling of pain.  However, it should be noted that some philosophers subscribe to a weaker version of the doctrine.



The True Non Reductive Materialism: Agnostic Materialism

In rejecting ontological physicalism what materialist credentials are open to a theorist who is committed to a materialist ontology?  Recall that a physicalist holds that the universe is constituted of particles, fields and force (energy) and the laws that govern their behaviour.  Physicalism individuates particulars by reference to their extrinsic properties, i.e., in terms of their functional relations to other particulars.  Our principal objection to physicalism is that it does not take adequate notice of the integrity of experience.  Experience is dissolved into something we-know-not-what except for its relationships to stimuli and responses.  Thus Armstrong stipulates, ‘The concept of a mental state is the concept of that, whatever is may turn out to be, which is brought about in a man by certain stimuli and which in turn brings about certain responses’18.  Physicalism holds that there is nothing to experience except for its relational properties.


Contrary to the physicalist precept according to which to have (say) a headache is to be disposed to exhibit a certain pattern of relations between stimuli and responses, we are being urged to consider other options for individuating mental events types, such as the way the headache type is felt by the subject that has it. The brand of materialism that is being canvassed as the alternative to the physicalist relational interpretation of mental events (states, properties) disengages the felt qualitative character of a given conscious mental type from its relational properties.  It upholds that a headache type presents itself to the subject that has it, with a certain felt quality.  It is in terms of its felt character that the subject picks out the headache type.  This mode of individuating a headache type, as with all other occurrent experiences, is independent of the relation interpretation that physicalism puts on the conscious event type.  This felt quality of the conscious event type does not figure in physicalism because physics has no conceptual tool to deal with the felt qualities.  However, if we cannot say what role felt qualities play in the functional network of physical systems that experience headaches and exhibit headache behaviours, that failure is not evidence for the denial of the occurrence of felt qualities.  Rather it could be argued that with a certain felt qualitative content, conscious mental events ought to be individuated primarily by the felt character peculiar to its event type.





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