Philosophers in the materialist tradition had little option but to accommodate the new directions that physics had taken in the twentieth century. It became clear that ontology – discovering what exists – is a matter for science, rather than philosophy. Philosophers have played a part by bringing some conceptual clarification to the bizarre and paradoxical world of current physics. Such philosophical work, to be valuable, has to be predicated on an understanding and appreciation of the physics, and to that extent it is philosophy undertaken within physics. Conceptual clarification is a necessary part of physics.
Most philosophical work in the materialist tradition since the rise of the new physics has focused on the nature of psychological phenomena, these being the greatest challenge for materialism. There is a vast and growing literature in this area of metaphysics, but it is possible to identify two central and very different approaches to the challenge. Both have at times adopted the new name physicalism in place of materialism, but with radically different ideas about how this title is to be understood.
They can be initially identified as reductionist and non-reductionist approaches to psychological phenomena. Reductionist approaches attempt to demonstrate that, appearances notwithstanding, psychological phenomena are in fact material. Non-reductionist approaches deny the feasibility of the reductionist approach and seek to retain the spirit of materialism while acknowledging the existence of non-material psychological phenomena. In this chapter a representative example of each approach will be described.
The reductionist theory is known as mind-brain identity theory, or mind-body identity theory, and hereafter in this chapter will be referred to simply as identity theory. It wears its nature on its sleeve. It seeks to say, in some way or other, the mind and the brain are the same thing. This theory is examined in the next section.
The non-reductionist theory can be called supervenient physicalism. Like identity theory, it makes some quite radical claims and in many ways it can be seen as less like traditional materialism than identity theory, but more in tune with contemporary physics. Both theories require a confrontation with the bizarre, and both theories leave some cherished beliefs about human beings under a cloud of doubt.
From the perspective offered here, one approach is considered more successful than the other. Identity theory has, to all intents and purposes, had its day, if a strict accord with modern physics is taken as a requirement of physicalism. However, this is a statement that will be considered contentious by many. Furthermore, the central concept of the other approach, supervenience, has its own critics with regard to its theoretical value. It can be challenged as offering more mystery than explanatory power.
So, in summary, the path divided, but as physicalists, as inheritors of the materialist tradition, the central preoccupation for both traditions was the characterisation of the apparently non-material phenomena of the world. And the seemingly non-material phenomena of greatest concern were the psychological phenomena of our human experience. While the approaches differ profoundly, neither one provides much solace for our cherished self-image. The human being who emerges in these physicalist accounts may not feel to be quite what human beings imagined themselves to be previously.
The discussion draws on the introductory essay in Modern Materialism: Readings on Mind-Body Identity, edited by John O’Connor (1969). The book contains foundational papers in identity theory, not only by the founders of the tradition, but also by some of the biggest names in twentieth-century analytic philosophy. This shows how central this project was for analytic philosophy in the latter part of the last century.
The introduction clearly describes the landscape in which this theory has been developed. It is presented in three principle sections. The first, ‘Man and Nature’, makes clear that in parallel with the more general materialist perspective, identity theory focuses specifically on the question of the nature of the human being. O’Connor poses the rather vague question ‘Is man like or unlike the rest of things in the world?’ as a starting point for contrasting the materialist identity theory with the non-materialist view discussed here in earlier chapters that sees the human being comprised of a material body and a non-material soul or mind. All materialists will concur with O’Connor in seeing man as ‘like the rest of things in nature’, but seriously question the following step in his argument:
… science is more and more able to explain so-called mental phenomena on the basis of physical laws, as is shown by recent work in the chemical basis of schizophrenia, for example. They also note that computers seem more and more capable of approximating what men call rationality. On this basis, [materialist] philosophers conclude that an adequate account of human beings can be given in terms of sciences that seem to be capable of producing adequate accounts of the rest of nature.
(p. 4)
Clearly much hangs on the notion of explanation, but nobody today would seriously suggest that finding neurophysiological correlates of the symptoms associated with schizophrenia could be described as an explanation of schizophrenia. Equally, O’Connor employs the rather suspect notion of adequacy – what are the criteria for adequacy of an account of some phenomenon?
The second section, ‘Physicalism’, introduces O’Connor’s understanding of how materialism found itself obliged to undergo a change of name. Describing materialism as the view
(1) That man is like nature in that both consist of the same materials – those materials studied by natural science, in particular physics – and (2) that an adequate account of human beings expressed in terms of a scientific theory is a complete and adequate account.
(p. 5)
In the past this was called materialism, but
in its modern form, it has become known to philosophers as physicalism. This is perhaps a better name for it, since ‘materialism’ suggests that everything is made up of matter and contemporary physics has shown that there is a lot more to the world than matter; indeed, the line between matter and force is anything but sharp. The word ‘physicalism’, on the other hand, seems more flexible; it merely suggests that man, whatever he is, can be described adequately with the terms and concepts employed by the science of physics.
(p. 5)
The suggestion seems to be that the change of name does not signify anything more profound than a recognition that physics recognises more in reality than matter. The lessons from physics are limited to this. But referring back to Chapter 5, it will be recalled that the revolution in the understanding of the world arising from the discoveries of twentieth-century physics has more far-reaching consequences than this.
O’Connor goes on – the ‘program’ of physicalism involves two tasks: first to ‘indicate what form a physicalist account of human beings might take’, and second ‘to demonstrate that there is no difficulty in principle in the adoption of physicalism’. With regard to this second task, O’Connor writes
[the physicalists] are concerned to show that physicalism offers at least a possible account of human beings … the chief objection to physicalism is that it offers no way of accounting for the mental life of human beings. Minds are not physical, it is argued, and consciousness is not a physical property. Since human beings have minds and are conscious, physicalism is bound to be an inadequate view. Given the seriousness of this charge, it is not surprising that philosophers who are sympathetic to physicalism spend much of their time and effort attempting to show that the charge is not true.
(pp. 7–8)
O’Connor cites three ways physicalists characterise mental phenomena – the first claims that all mental terms stand for entities, and these entities are physical; the second, known as eliminitavism, denies there are any such things as mental entities at all – ‘to have a mental life according to this theory is just to be disposed to behave in certain ways in certain circumstances’. The third, generally preferred by the majority of identity-theory physicalists, finds a path between these two extremes. A feature of such a theory would be to understand a person using mental terms as ‘speaking of experiences that human beings have but not of “mental entities” that human beings experience’:
There are no such things as pains in the world, but there are experiences we call ‘being-in-pain.’ (The physicalist might then go on to say that the experience of being-in-pain is really a physical process.)
(p. 9)
In addition to an account of the mental, an account of the physical is required also, in the specific context of groundwork for the identity theory. O’Connor claims that most contemporary physicalists hold that
The physical aspect of man that is relevant to an account of his mental life consists of both his body (considered in macroscopic behavioural terms) and his brain and central nervous system. These philosophers believe that if some mental terms can be analysed in terms of dispositions to behave in certain ways and others can be understood as referring to experiences that are really physical processes, then the physicalist position is in very fine shape.
(p. 11)
O’Connor’s third section, ‘The Identity Theory’, highlights how complicated the philosophy of identity can be. In particular, four issues arise. The first is to ask if the identity mooted is necessary, like ‘2 + 2 = 4’ and ‘All bachelors are unmarried’, or contingent, like ‘The table is made of oak’. Identity theory is bound to deal in the contingent kind of identities; its claim cannot be based on the meaning of terms.
Second, there is some dispute as to whether the identities of concern are arrived at by a process of discovery or a process of decision. It would seem that identity theory implicitly imagines an identity to be discovered, but it may too be hard to conceive of a ‘discovery that could show that things such as experiences and brain processes are identical, as opposed to being merely constantly correlated’ (p. 13).
Third, and much more contentious than the first two, concerns the strength of the identity claim. O’Connor describes strict identity only if two things share all their nonmodal properties. But something here won’t do – strict identities involve only one thing, perhaps going by different names, or different descriptions. The famous example in philosophy is ‘The Morning Star is the Evening Star’, as the descriptive terms both refer to Venus. Science poses a difficult version of this issue – is the table identical with the cluster of atoms that comprise the table? The table is still but the cluster is in constant motion. The identity theorists may argue on this point:
This has led some philosophers to say that the sort of identity that might suffice for a physicalist is some sort of theoretical identity, an identity based upon a scientific theory … Whether an identity can be defined this loosely and yet actually remain an identity is a moot question. Some philosophers feel that anything short of strict identity would be merely a correlation of two things, and this would not be sufficient for an identity theorist.
(p. 14)
The fourth, equally important, issue concerns the question of whether the identities are general or particular. In philosophy this distinction is often identified as a choice between token and type identity. So the issue is this – is identity theory making a claim that there is a token identity statement that can be made linking a particular mental entity, event or process with a physical entity, event or process (that is, they are the same thing under different descriptions), or is the stronger claim being made that mental entities, events or processes of a given type A are always identical with a physical entity, event or process of type B? It would look as though identity theorists would want to make the stronger claim, but it may be possible to develop a theory that includes both general and particular identity statements.
O’Connor next turns to the question of the precise detail of the identity claim – what is being said to be identical to what? By far the most widely accepted answer is that there are identities between experiences and brain processes:
According to this theory, there are no mental entities, but there are experiences – for example, having an after-image. This experience is identical with some brain process. Which particular process it is may require a lot of neurophysiological investigation to discover, of course. The identity theorist does not claim merely that whenever a person has a certain after-image he is undergoing some brain process, for this view could be held by a dualist. Rather he claims that the experience is the brain process. There is one thing and not two.
(p. 16)
This is, in essence, the perspective offered of identity theory, and its merits and deficiencies need to be judged in order to ascertain its place in the long history of materialism.
It does, at first sight, to be a rather strange theory. At first sight, it would seem to be obvious that mental experiences are not brain processes; they are, evidently, different types of thing. There may be correlations between mental experiences and brain processes, but to make an identity claim seems profoundly counter-intuitive.
Of course, identity theorists recognise that the theory involves a radical challenge to intuition, and while it seems these intuitive criticisms of identity theory have considerable force, identity theorists would argue vigorously that these objections can be met. The arguments are not pertinent to the present purpose, but there is another kind of criticism that would seem to be potentially decisive.
To go back to square one, the point of identity theory is to defend materialism, and the way is to show that apparently non-physical things are in fact physical after all. And the things the apparently non-physical things are identified with are brain processes. But what is the essence of the materialism that is being defended? Originally it was some version of an ontology of atoms in the void, but this has had to be abandoned, because materialism has always been obliged to take the lead from science, as scientific discovery arises from the same epistemological methodology that materialism espouses, and science has abandoned the atoms in the void ontology. What the identity theorists fail to take on board is just how profoundly science has abandoned traditional materialism. They talk as if brain processes – dynamic systems of neuronal networks – carry, for science, the full ontological status once ascribed to the atoms in the void. They imagine that the atoms and molecules that in composition form the brain processes supposedly identical with mental experiences are given by science unambiguous status as entities that exist. Indeed, science does acknowledge their status as things that exist, but no more than thoughts and feelings; the implicit ontology of contemporary physics recognises these mental things as existing as much as atoms and molecules and neurones.
This is because these phenomena are not the fundamental elements of reality. In fact it is not known what these fundamental elements are, or what they are like. Taken at one level of scientific scrutiny a world of atoms and molecules is discovered and described. At another – higher – level psychological phenomena are found. In the search for the deepest structures, work goes on – in quantum gravity, in string theory and perhaps other as-yet-unsung approaches.
A leading contemporary philosopher, Tim Crane, has written in the Times Literary Supplement some words the defenders of materialism are obliged to take seriously.
We know, with as much certainty as we know anything, that we have conscious thoughts and experiences; we have memories and dreams, we imagine, desire and regret things; we plan our actions and form intentions; we form emotional attachments and structure our lives around them. All of these things are underpinned, in a way that we do not yet understand, by the unbelievable complexity of the brain and its mechanisms, some of which extend into the body. We need to make connections between the knowledge that we have about our minds and the knowledge that we have of our bodies and brains: but we do not yet know how to connect this knowledge in a systematic, illuminating way.
In order to make these connections, we must first accept the irreducible reality of the mental, or psychological, for what it is. To connect two things, these things must both exist. Psychological reality is not a separate ‘substance’, and it is not just matter either. Our psychological states and processes are as real as anything going on inside us – as real as our weight, our metabolism, our body temperature – and the fact that they are invisible is no more an objection to their existence than the fact that our weights and temperatures are invisible is an objection to theirs.
Some will protest that this is all very well as a way of speaking, but in reality ‘all there is’ to the mind is the brain, and this psychological talk is just that: talk. Sometimes you hear scientists saying that psychological reality is just another ‘level of description’ of the brain. But this is sloppy thinking: our dreams, experiences, thoughts and intentions are not ‘descriptions’. They are events or processes going on in us, as real as the neural activity with which they are correlated.
(TLS, 26/5/17p.8; emphasis added)
It may be surprising that this clear, seemingly obvious account of the situation needs to be stated at all. But it does – in some philosophical and scientific circles versions of identity theory remain influential, despite their flaws, and despite being in conflict with the perspectives of contemporary science and contradicting the evidence of our experience as human beings. Crane sees himself arguing against materialism, but in the next section it will be shown that a coherent physicalism can be expressed that is true both to the spirit of materialism and to every word in the quotation from Crane.
There is a considerable amount of work in contemporary analytic philosophy on non-reductive formulations of physicalism. The authors of the present work have offered one formulation, and it is this that is presented here in outline (Brown & Ladyman, 2009). For readers wishing to explore the field, Justin Tiehen’s paper ‘Recent Work on Physicalism’ (Tiehen, 2018) provides a very useful summary of the competing formulations, together with numerous references.
The presentation of supervenient physicalism will be approached in stages. The first stage, elements of which will be modified in the final formulation, begins of necessity with supervenience and its associated concepts.
From here on, discussion of matter will be replaced by discussion of the physical. The physical is to be understood as that which is referred to in theories of physics. These theories do not, and it is forecast will not, ever posit psychological or spiritual phenomena.
The concept of supervenience is central to twenty-first-century physicalism, and while it is not a particularly complicated idea, it can nevertheless be difficult to grasp. It is a concept that is embedded in a broader theoretical perspective, and it is going to be helpful to outline certain fundamental ideas on the basis of which supervenience takes its role in physicalist theory. Because of the limitations of space, the following is inevitably a rather impressionistic account of the field, but it should be sufficient for an intuitive grasp of the physicalist world view.
(a) Change. The notion of change is widespread in everyday discourse, and for present purposes there is no need to elaborate the basic idea. It is a familiar idea to think that a thing can change in some way or other and still retain its identity as that thing. The table can become wobbly, but it is still that table. A person can grow old, or become more placid, while still being that same person who was there before the change.
There is one important distinction philosophers draw between kinds of change, and this relates to the distinction between internal and external properties. The table may have the internal property of being made of teak, and the external property of being five metres from the bookcase. If the bookcase is moved the external property mentioned will change – the table will now be six metres from the bookcase, although its internal properties will have undergone no change. The primary concern here is with internal properties.
(b) Levels of reality and the hierarchy of sciences. These issues are very complex and contentious. But one clear lesson learned from the scientific revolution of the past 500 years is that reality is much more complicated than it may be imagined to be from basic observation by way of the senses. The atomists’ idea that all material things are composed of tiny material things has been completely superseded by the rise of atomic and molecular chemistry. As was described in the last chapter, the concepts used in the description of the world of everyday things – tables and trees, people and lions, buildings and cars, basically of medium-sized objects occupying space – are unsuited for the purpose of describing the atomic and subatomic world, as discovered through the advances of theoretical physics and observed through the senses augmented by scientific instruments.
Yet in some way that bit of reality identified as the table is also an object that can fall under the description offered by the physics of condensed matter in terms of atoms and molecules. Reality can be conceived of as layered, and there is a hierarchy of human theories appropriate to the corresponding layers of reality.
Of course, in some basic sense, reality is not layered, it just is. It is conceived of as layered from the viewpoint of human knowledge and understanding. Human knowledge brings an understanding of the table – its weight, its material constituents – teak, for example – its method of construction, its use and purposes. But human science also provides information with regard to its constituent atoms and molecules, its composition in terms of elements and the way that it exhibits solidity to human touch. And theoretical physics is preoccupied with bringing an understanding of the sub-atomic world underlying the atomic and molecular structure of the table. Furthermore the hierarchy itself is complex and simple models of the reduction of the sciences to physics have also become completely outdated.
(c) The special sciences. Physics is taken to be the most general science that concerns itself with all phenomena. In contrast, consider sciences such as economics, or biology, or psychology. These sciences concern themselves with a subset of real phenomena. Biology is the science of life; its concern is the nature of living things. Economics is concerned with economic phenomena – markets, money supply, interest rates, levels of supply and demand, gross national product. It enters the realm of psychology, the science of psychological phenomena, in its concern with the decision-making processes of consumers. These are the behavioural sciences.
The suggestion here is that there is a hierarchy of sciences. It is not a completely neat structure; the special sciences overlap and share concerns, but physics is seen as the foundational science upon which the others are built. And physics itself can be seen as layered. The mechanics of solid objects is part of physics. The term fundamental physics can be used to identify the work seeking to understand and describe the more fundamental structures of reality.
The consequences of the layered picture of reality are significant. Consider our everyday ‘science’ of the objects in our houses. According to this theory, tables are solid and will support the dinner plates. What is discovered at the atomic level is that the table is not solid; the atoms on which it is composed are not dense in any everyday understanding of density. The slice of space-time housing an atom is largely empty. However, atomic theory provides an explanation of why the table supports the dinner plates. An account is given of how a network, or web, of atomic forces creates the property of solidity – that is, the property of supporting the dinner plates. Atomic science and table science both acknowledge the property of supporting the plates, but they each have different stories to tell about the nature of that property. Table science says it is because the table is dense; atomic science says it is not dense but held together by powerful atomic forces.
On the basis of these ideas, the concept of supervenience can be described. Here is a provisional definition:
A supervenes on B if there can be no change in A unless there is a change in B.
A and B are left undefined; they may be properties or things, or even levels of reality. Referring again to the table, there can be no change in any feature of the table observed by the dinner guests without there having been some change in the subatomic structure of the table. If the table has become warmer, the atoms couldn’t possibly be just as they were when the table was cooler. To expand on this idea, consider the following statements:
The beauty of a work of art supervenes on its material form.
It is not possible to imagine a situation where two pictures are identical except that one is beautiful and the other is not. Notice that a strong concept is involved – ‘identical’ means what it says. Now, it may be argued, two things can’t be truly identical. Referring back to the paragraph on change, if they are separate entities, they are going to have differing external properties, for a start. But they are also going to have different internal properties; if they are paintings, they will be on different canvasses; if sculptures, they will be made of different pieces of stone.
These objections are perfectly reasonable, and philosophers draw on further complex ideas to circumvent the objections in order to convey the idea. So a philosopher may imagine our reality, R, and a separate possible world, W, like R in all respects except that the painting is beautiful in R and not in W. And he may claim that W could not possibly exist. Notice this is not about whether people think the painting is beautiful or not; it is about whether the painting is beautiful or not. Now a step further:
The mental phenomena of an individual supervene on her material constitution.
It is not possible to imagine that two people are alike in every way – in particular, the material constitution of their bodies is precisely the same – and yet one thinks the painting is beautiful and the other does not. Or one is happy and the other is sad. Once again, the philosopher would turn to possible world analysis to render this idea coherent, but the point is made with regard to the concept of supervenience – there is a fundamental dependence the supervenient entity has on the underlying, subvenient entity.
It is at this point that the place of supervenience in physicalist theory may become clearer, for it is evident that if mental entities are supervenient on non-mental, physical, subvenient phenomena, the existence of a soul, or spirit, independent of, autonomous from, the body, is thereby denied.
If the lessons of contemporary physics are incorporated into this perspective, a more general statement can be made sufficient for the purpose of expressing physicalism.
Any non-fundamental property, event or entity supervenes on the subvenient reality underlying it.
As an instance, all the everyday, medium-sized objects that are familiar to us from our ordinary perception of the world supervene on the underlying, subvenient world of the very small. And as a further, critical instance, it is claimed:
All the psychological phenomena of the world supervene on all the non-psychological phenomena that are subvenient to them.
A more formal statement of the philosophical position of physicalism is this:
Given the real world R and all possible worlds,
(i) In any world W where there is a difference from R in a mental feature, there will also be a difference in W from R in some physical feature;
(ii) There is a world W that is physically different from R but which has identical mental features to R.
It is important to understand the importance of the second paragraph of this definition. Supervenience is an asymmetric relation. It affords a primacy to the fundamental, the most basic, features of reality.
But what is meant by the term ‘physical’? Here the philosophical physicalist is obliged to openly avow her humility, because as a philosopher she has no means at her disposal to answer the question of what exists. She is obliged to demur to the natural scientist, the physicist, to provide the answer. The physical – what exists – is what science tells us exists.
Science may acknowledge two kinds of existent – existents supervenient on more fundamental elements, or fundamental constituents of reality beneath which there is nothing. Nobody in modern science has yet proclaimed the discovery of the fundamental level, but one day it may be reached, and if it is reached, the science will need to provide compelling evidence as to why it is fundamental and not, at least potentially, supervenient on deeper structures. It is worthwhile to consider the possibility too that it may not be possible for human science to apprehend the fundamental level – that there may be genuine limits to our knowledge – and it is interesting to consider the possibility that there may not be a fundamental level at all.
What has become clear is that as physics explores reality at ever smaller orders of magnitude, our ordinary concept of object, a body existing in space, becomes hopelessly inadequate. It was seen in the last chapter how the world of things existing in time and space has to be relinquished for a far more complex and subtle conceptual landscape that can seemingly only be described in an abstract mathematical language.
The physicalist claim boils down to a prediction in two parts – first
(i) that physics will neither discover a psychological entity at the deeper layers that it explores;
(ii) that physics will not posit the existence of an entity purely for the purpose of accounting for psychological phenomena.
Identifying the physicalist claim in this way, it makes clear that physicalism is a theory that could be proved false – the hallmark of a valid theory in science, and a hallmark of the kind of metaphysical theory that physicalism seeks to be.
A word about the second part of the prediction is in order. Its inclusion in the definition of physicalism is prompted by an idea in the biological sciences. The idea can be traced back to the ancient world, but in the eighteenth and nineteenth centuries there was a central ongoing dispute among biologists concerning the question of whether or not living things were fundamentally different in some crucial way from inanimate things. People who believed there to be a fundamental distinction to be drawn came to be known as vitalists, because the special property attributed to living things was a property of a mysterious, possibly non-material kind that gave to beings with the property the property of being alive – the vitality of life. All kinds of words and expressions came to be used to identify this special thing, the most popular coming to be a term coined as late as the early twentieth century by Henri Bergson. The élan vital was the name given to that property of living things that accounted for… their life. It is the positing of such a property, or entity, for the purpose of accounting for psychological phenomena that the second part of the prediction claims will not happen. Eventually vitalism was taken by the vast majority of biologists to have been refuted by empirical evidence, and was to be banished from science. But it attracted some first-order scientists, including Louis Pasteur, and of course the bridges that were finally laid linking chemistry directly with biology were far more sophisticated and complex than the attempts at a mechanistic account of life that vitalists criticised, reasonably enough, for being hopelessly inadequate for the provision of an explanation of the phenomena of life.
For reasons that will become clear, it is important to distinguish two approaches to the definition of supervenience. The concern here is with a theory that supports a physicalist outlook, and for that purpose a global supervenience is sufficient – all the psychological features of reality supervene on the underlying, subvenient base. Local supervenience, in contrast, seeks to link particular features of the higher layer with particular elements of the deeper layer. Such an approach makes obvious sense if we consider, again, the table. The table of our house supervenes on its constituent atoms.
But things may not be so simple or obvious in general. Take the mind of an individual person – what is the subvenient base of this mind? There are a number of answers on offer; some would say the individual’s brain is the subvenient base; others might say it is the entire nervous system of the individual, and yet others would point to the entire body of the individual as the subvenient base. Even more controversially, some theorists argue that the individual mind supervenes on a broader subvenient base that extends beyond the boundaries of the individual’s physical being.
There are many problems with local supervenience. The primary one is that there is no clear set of philosophical criteria to help in the task of choosing between these options. There is interesting and important empirical research that is exploring the link, for example, between a person’s wish and the associated processes in the person’s musculature and nervous system. This research is promising extraordinary technological advances, such as the ability to have the prosthetic mechanical arm of an amputee respond according to the person’s wish. It is in science and technology that local supervenience can be seen to be a useful perspective. With issues of the kind science and technology struggles with, the philosophy of local supervenience is basically guesswork.
There is a deeper problem. In its philosophically most rigorous form, supervenience does not point to the supervenience of something on the layer immediately beneath it; the objects and properties of one layer supervene on all the layers that underlie it. This formulation is needed for a specific reason.
One feature of the layers of reality is that deeper layers bring greater complexity. For example, there is the single table, beneath which there is a structure of trillions of atoms. That structure of atoms supervenes on an even more complex array of subatomic entities. Just as the observable state of the table could arise from any one of a large number of potential states at the atomic level, so any given state at the atomic level might supervene on any one of a vast number of sub-atomic states. Now here is the vital theoretical possibility.
Suppose:
A supervenes on B, and B supervenes on C;
A is in state a1 and B is in state b1;
When B is in state b1, C is in state c1;
It is possible that C changes to state c2, thereby causing an alteration in the state of A from a1 to a2, while B remains unchanged in state b1.
An example of the possibility being suggested is this: that a change in the mental state of an individual may not be identified with a change at the level of the neuronal network of the person’s brain, but may be related to a change at a deeper level that does not find expression in the neuronal map available to neuroscience.
Global supervenience makes a much weaker claim than local supervenience, but it is all that is required for physicalism. It is in the character of physicalism to assign to science and technology the task of exploring the specific links between the layers of reality, as when neuroscientists link the nervous system and a thought, or atomic physics accounts for the chemical bond.
Global supervenience is also weak in another sense: it does not have anything to say about the specific nature of the supervenient relation present between any given supervenient-subvenient dyad. Nothing is known about the comparison of the relation, on the one hand, between mind and the underlying layers, and, on the other hand, the relation between the material object and the underlying layers – except that they are both supervenient relations. However, the following section draws attention to the disturbing consequences of the strength of global supervenience.
The situation looks paradoxical. On the one hand, an ontological theory, materialism, has been superseded by a theory, physicalism, that claims it has no tools with which to make positive ontological claims. On the other hand, physicalism claims to be the natural successor of materialism and to capture its essence. That does make it sound as though the essence of ontological materialism was not ontological, but it’s not quite a bad as that. The ontological theories of the materialists can be seen as primitive attempts at science, without all the conceptual and concrete tools of modern science, and with all the innocent optimism that scientific discovery was readily available to the acute observer with a sound capacity to reason. No one could really have predicted just how obscure, paradoxical and baffling the nature of reality would prove to be.
However, the formulation of physicalism outlined above has met with a formidable argument that will expose just how radical physicalism is with respect to our everyday, cherished beliefs about our nature.
The argument is called the causal exclusion argument. It challenges the intelligibility of mental causation, and it can be expressed like this: if a mental event M supervenes on a physical event P, and P causes a further physical event P* on which a further mental event M* supervenes, serious doubt can be cast on the claim that M causes M*. The account at the physical level of how P causes P*, together with the supervenient relations, is sufficient to account for the occurrence of M*. The M-to-M* doesn’t seem to be a genuine causal relation.
The philosopher Jerry Fodor has expressed a personal response to the problem in no uncertain terms:
… if it isn’t literally true that my wanting is causally responsible for my reaching, and my itching is causally responsible for my scratching, and my believing is causally responsible for my saying … if none of that is literally true, then practically everything I believe about anything is false and it’s the end of the world.
(Fodor, 1990, p. 156)
Here’s a situation that may clarify what has worried Fodor so much. Imagine you are deciding whether or not to open the window. It seems as though the world has reached a fork in the road – on one possible future path the window stays shut, while on the other possible path the window is opened; furthermore, it seems as if you hold in your hands, in your choice, which path the future will take. However, if the subvenient base of your deliberation stands in a causal role to the subvenient base of your subsequent decision – to open or not to open – then you would seem to lose your central place in the story. What happens – window opened or window kept shut – can be determined without reference to the supervenient story of you and your deliberations.
Fodor’s anxieties are not without foundation. It was looking very promising. In outline: the materialist relinquishes the search for what exists to the scientist, and simply predicts, on good inductive evidence, that the scientist will not posit psychological phenomena beyond those we are already familiar with. The materialist designates all phenomena, from quarks to thoughts, as things that exist but which are supervenient on some more, yet-to-be-discovered, fundamental level of reality. The materialist seems to have kept everything, including mental entities, at no cost. But in fact the cost, from Fodor’s perspective, is very high. But is it so high? Is it the end of the world?
The first point to be made is that this problem was always lurking in the shadows of materialism. Epicurus, and Lucretius after him, pointed to the swerve as the key explanatory feature of the reality of atoms in the void that would account for our freedom of will. However, no such account was forthcoming. Our intuitive account of ourselves as human beings seems to be implicitly a dualist picture where the individual can stand outside the material order and make free choices. It was observed above that the identity theorists demand a radical rethink of our intuitions about mental entities. What is clear now is that all materialist theories demand a radical rethink of what it is to be a human being.
This chapter concludes with the outline of an account of human choices and decisions intended to save the world. To begin, in addition to the supervenience of mental entities – thoughts, desires, deliberations and so on, there must too be actions. To clarify this idea, imagine a human being’s arm waving. This may be a simple event in the physical world, but it has become an action if it is a waving goodbye. An action is a physical motion of the body linked with an associated mental state.
On this basis, the deliberation about opening the window could have this analysis: you decide you want the window open; put another way, the wish for the window to be open forms in your mind. You then entertain the fantasy of the window being open and you have thoughts about the means to it being opened. Finally, on this basis, the action is undertaken to open the window.
It will not escape attention that this does not undermine the causal exclusion argument. Rather it simply provides a description of what is going on when we have the feeling that we hold the future in our hands. It does suggest that the opening of the window was based on our desire, but the roots of that desire can be traced at a sub-mental level. If the subvenient base of our minds is taken as our physical bodies, including the brain, it may be argued that this physical system ‘wanted’ the window open, and the mental wish expressed this. This perspective may explicate something of the identity theorist’s perspective, even if identity theory must be abandoned.