In recent years, analytic philosophers working in the metaphysics of mind have generally presumed that some sort of physicalism—the view that everything that exists, including the mind, is in some important sense ‘physical’—is mandatory. The supposed completeness of physics or—a close variant of this—the supposed causal closure of the physical is one consideration often given in favour of physicalism. The thought runs that if all the causal goings-on in the world can be accounted for physically, then there doesn’t seem to be any reason to posit the existence of a mind that is in any sense something ‘over and above’ and distinct from the physical world.
One alternative view to ‘physicalism’ is dualism, which holds holds that there is some important sense in which mental goings on—psychological states such as having beliefs or desires; perceptual experiences such as seeing a bright red strawberry, or hearing a loud bang, and sensations such as feeling a sharp pain in your knee, or a nagging itch on your back—are in important ways distinct from physical goings-on such as neurophysiological states of the brain.
Physicalism comes in a number of varieties. One approach to physicalism is strongly reductionist, claiming, say, that mental goings-on should be identified with (i.e. are the very same thing as) brain states, another is weakly non-reductionist, taking mental goings-on to be distinct from, but in some sense strongly dependent on, brain states. In any case, either physicalist position excludes anything worthy of the title ‘strong ontological emergence’, where mental properties and states are concerned. This consensus has begun to be challenged and disrupted recently, partly in the light of new developments in the metaphysics of causation, but also because metaphysicians of mind are beginning to look more carefully at what current physics, including quantum mechanics—as opposed to some simplistic version of classical Newtonian mechanics—actually implies with regard to the causal and ontological status of complex macroscopic objects, properties and systems. Now that it is increasingly acknowledged that quantum mechanics cannot simply be dismissed as irrelevant to the metaphysics of mental causation, on the spurious ground that it applies only to physical systems many orders of magnitude smaller than neural structures in the brain, its implications need to be taken seriously in the philosophy of mind.
Let’s begin by looking at the various different positions that philosophers have adopted in the debate concerning the status of the mind, and how it relates to the physical world.
Varieties of physicalism about the mind
There are a number of different ways that the core claim of physicalism about the mind—that there is nothing about minds that make them in some sense ‘over and above’ or distinct from the physical world—can be elaborated upon.
One way of expanding on this claim is simply to identify types of mental goings-on—say, being in pain—with some purely physical state of affairs—say, c-fibres firing. On this account, any occurrence of pain is simply the occurrence of a certain neurological event, the firing of c-fibres. This is known as the Type-Type Identity Theory, and it says that mental goings-on just are physical goings-on, and so there is no sense in which they can be strongly emergent from them.
Another way of formulating the physicalist position is to claim that whilst we can’t identify types of mental goings-on with types of physical goings on, we can identify each and every particular mental occurrence with a physical occurrence. On this account, it’s possible that there’s some occurrence of pain without c-fibres firing, but not without some neurological occurrence or other—say, perhaps, some other nerve-fibre firing. This is known as the Token-Token Identity Theory, as whilst it does not identify types of mental occurrence with types of physical occurrence, it does identify individual token mental occurences with individual token physical occurences.
Both these varieties of physicalism are ontologically reductive—they take apparently mental goings to be nothing but physical goings on. According to both Token-Token and Type-Type Identity Theorists, all there is to our mental lives is the occurrence of certain complex physical goings-on.
This can be contrasted with non-reductive physicalism, which holds that mental goings-on cannot be identified with physical goings-on, and so cannot be reduced to them. However, nor are mental occurrences independent of physical occurrences. Rather, there is some relation—sometimes specified as supervenience—between the mental and the physical. This position is considered a variety of physicalism because it holds the physical to be somehow prior to the mental; for non-reductive physicalists, the mental depends in some important sense upon the physical. However, some find it hard to see how such a position can really be distinguished from some form of dualism about the mind and body.
Varieties of emergentism about the mind
In contrast to physicalist accounts of the mind, emergentist positions hold that there is some sense in which mental goings on are distinct from, and in some sense something ‘over and above’ physical goings on. Like physicalism, however, emergentism can come in a variety of forms.
First, it is important to note that whilst emergenist positions will generally be dualist, in that they take there to be some genuine difference between the mental and the physical, not every dualist position will necessarily be emergentist. The characteristic feature of emergentist positions is that they take there to be a relation of emergence between the mind and the physical world from which it emerges. Some dualist positions might, whilst they agree with emergentism that there is a genuine difference between the mental and the physical, not take any such emergence relation to obtain.
The core commitment of dualist accounts of the mind and body is that there is some radical difference between the mental and the physical. Perhaps the most famous dualist is French Rationalist philosopher, mathematician and scientist René Descartes (1596-1650).
Descartes argued that, as we can imagine our minds existing separately from our body, and our body existing separately from our minds, then these two cannot be identified. On this basis, he took the world be made of two fundamentally different substances— what he called res extensa (meaning ‘extended stuff’ in Latin) and res cogitans (meaning ‘thinking stuff’). One big challenge for Descartes was to explain how these two substances could possibly interact.
Many modern dualists reject the idea that there are two kinds of substance in the world. Instead, they take there to be two kinds of property—what we call the mind is characterised by mental properties, and the physical world is characterised by physical properties. For instance, it is sometimes argued that the properties that characterise our conscious experiences— what it is like to see a bright red tomato, or to hear a high-pitched sound, or to taste apple pie—cannot be accounted for by appeal to physical properties—such as mass and charge—alone.
One way emergentist positions on the mind can differ is in terms of whether they are strong or weak. Another important way emergentist positions about the mind can be distinguished is in terms of what sort of entity they take to be emergent. Emergent property dualism would hold that whilst mental goings on don’t require us to posit any new object or substance, suitably complex physical arrangements give rise to new kinds of properties—ways that things are—which are mental in nature.
On this view, for instance, when certain physical systems reach certain levels of complexity, such as that found in the human brain, properties are generated which are so different to typical physical properties (such as mass and electrical charge) that they should be considered of a different kind, as distinctively mental. For instance, it might be thought that beliefs, which have the feature of being about something or other (about what time it is, or about which sport team will win the cup this year, say) cannot be considered physical, as no typical physical properties have this feature of being about something (what is sometimes called in the philosophical and psychological literature intentionality).
This can be contrasted with emergent substance dualism. A number of contemporary philosophers of mind—still very much in a minority—have begun to develop this sort of position (for instance, Koons & Bealer (2010)). According to this view, when physical systems become suitably complex, not only new properties but also new bearers of properties—new kinds of objects, with their own distinctive persistence conditions and characteristic causal powers, irreducible to the persistence conditions and powers of aggregates of microphysical objects—come into existence, with persons (that is, persisting subjects of thought and experience possessing powers of intentional agency) providing a central, but perhaps by no means unique, example.
When you feel thirsty and reach for a drink, can your feeling of thirstiness ever be the cause of your reaching for a drink, or is it all just neurons firing?
Accounting for how the mind can bring about effects in the physical world is a deep and interesting philosophical puzzle. It is often held to be a particularly difficult one to solve if one is committed to any form of emergent dualism about the mind.
Our everyday experience suggests to us that sometimes, mental goings-on make a causal difference to physical goings on. My desire to take a drink, plus my belief that there is coffee in my mug—both of which seem to be mental goings-on—are, it might be thought, the causes of my reaching out, picking up the mug and taking a sip—all of which seem to be physical goings on.
Often one of the advantages those who hold a reductive physicalist view of the mind claim for their position is that, if mental goings-on are nothing more than physical goings-on, then there’s nothing mysterious about this—we’re used to seeing physical things cause other physical things all the time!
However, it is thought that apparently mental causation poses more of a challenge for both dualist positions (whether emergentist or non-emergentist) and for non-reductive physicalism.
One of the puzzles that mental causation raises is the interaction problem—if mental entities (whether substances, properties, events or some other kind of thing) are genuinely different sorts of entity to physical ones, then how is it that they are able to causally interact with physical entities? Furthermore, if claims about the causal completeness [link] and closure of the physical [link] should be taken seriously, then this seems to threaten the status of mental goings-on as causes—for if every physical effect already has some physical cause (which will be distinct from the supposed mental cause), then it begins to look questionable whether supposed mental causes are really doing any of the causal work at all!
Excluding the Mind
In a physical world, what space is left for a mind that causes anything?
Jaegwon Kim (ref) has developed a powerful argument against the idea that mental states (and indeed, any higher level emergent states) can be the causes of either mental or physical effects. The argument was first developed to show that non-reductive physicalism cannot accommodate genuine mental causation.
The first step in the argument is the claim that every physical effect has some physical cause which is sufficient to produce that effect—that is, the cause is able to produce the effect all on its own.
The second step in the argument is the claim that, generally speaking, effects are not overdetermined—that is, that generally speaking, effects do not have more than one sufficient cause.
Given these two claims, consider a supposed instance of a mental state causing a physical effect—say, my desire to take a drink causing my reaching out and taking a sip of coffee. The first claim above implies that the physical effect—my reaching out and taking a sip of coffee—has some physical cause which is sufficient to bring it about—say, some particular neural state that my brain is in. Any position in the mind-body debate other than reductive physicalism holds that the supposed mental cause—my desire to take a drink—is distinct from this neural state. But the second claim above says that, generally speaking, effects—such as, my reaching out and taking a sip of coffee—do not have multiple sufficient causes. Given that there is a sufficient physical cause for the effect—the neural state that my brain is in—then the supposed mental cause—my desire—cannot really be a cause, because it is excluded from being so by the physical state.
If the first two steps of the argument are correct, then it seems that the only way mental states could be causes is if they are identical to physical states (as reductive physicalism claims); and that all other positions in the debate must accept that mental states cannot be causes of physical effects (this claim is sometimes called epiphenomenalism).
The Active Mind
However, not all philosophers are persuaded by arguments such as Kim’s that mental goings-on must either be reduced to physical goings-on, or else excluded from the realm of causation.
In the metaphysics of causation, new ways of thinking about both what causation really is, and what sorts of entities it involves, are coming to the fore, notably with the advocacy of new theories of ‘agent’ or ‘substance’ causation—challenging the consensus view that all causation is ‘event causation’, that is, a relation between one event which is a cause, and a separate event which is the effect stemming from that cause.
These thoughts are further developed by the formulation of new powers-based accounts of causation, which see ‘effects’ as the manifestations of the characteristic causal powers or dispositions of objects.
According to the powers-based approach, some of these manifestations may be generated spontaneously by a single object (one example of this may be radioactive decay), while others arise through the mutual co-operation of many objects possessing appropriately complementary powers and arranged in particular, appropriate ways in different specific environments.
If this is so, it now becomes possible to think that the basic loci of causation are in fact objects—that is, ‘substances’ or, in a broad sense, ‘agents'—rather than events, and that objects cause effects in virtue of manifesting their characteristic powers, whether autonomously or co-operatively. Moreover, given that higher-level objects such as are discussed in the special sciences—even if they can all in some broad sense be described as being 'physical’ because, for instance, they occupy regions of spacetime and have geometrical, kinematic and dynamic properties—are not now credibly conceived as mere aggregates, or mereological sums, of microphysical objects, such as the fundamental particles of physics. It also now becomes credible to suppose that such objects have causal powers which are not merely aggregations of the powers of their microphysical constituents and which, hence, can give rise to effects which can in no sense be seen as the mere results, in aggregate, of microphysical powers.
Thoughts along these lines seem to bear an important relation to the issue of emergence—if being in a particular mental state involves having some genuinely novel causal power which cannot be reduced to an aggregation of micro-physical powers, then perhaps arguments such as Kim’s Exclusion Argument can be resisted.
Scientific examples and the emergence of mind
One important question for the contemporary debate surrounding the issue of emergence and the metaphysics of mind is what the significance of scientific case studies is for the debate surrounding the mental and the physical. Examples such as superconductivity, certain phenomena that occur during phase-transitions in condensed matter and symmetry breaking in ferromagnets might well help to establish that there are some strongly emergent phenomena; that not all of reality can be accounted for in terms of fundamental physics.
However, it is not clear that one can move straightforwardly from such examples (leaving aside that they are contentious in themselves) to claims about the nature of mind. Even if scientific evidence suggests that strong emergence is required to explain, for instance, superconductivity, it might still be open to the physicalist to claim that mental goings-on (beliefs, desires, sensations and so on), regardless of the emergence of the superconductive, are themselves nothing over and above complex physical-goings on.