## 1. The Mind-Body Problem and the History of Dualism


### 1.1 The Mind-Body Problem




The mind-body problem is the problem: what is the relationship between
mind and body? Or alternatively: what is the relationship between
mental properties and physical properties?




Humans have (or seem to have) both physical properties and mental
properties. People have (or seem to have)the sort of properties
attributed in the physical sciences. These physical properties include
size, weight, shape, colour, motion through space and time, etc. But
they also have (or seem to have) mental properties, which we do not
attribute to typical physical objects These properties involve
consciousness (including perceptual experience, emotional experience,
and much else), intentionality (including beliefs, desires, and much
else), and they are possessed by a subject or a self.




Physical properties are public, in the sense that they are, in
principle, equally observable by anyone. Some physical
properties - like those of an electron - are not directly
observable at all, but they are equally available to all, to the same
degree, with scientific equipment and techniques. The same is not true
of mental properties. I may be able to tell that you are in pain by
your behaviour, but only you can feel it directly. Similarly, you just
know how something looks to you, and I can only surmise. Conscious
mental events are private to the subject, who has a privileged access
to them of a kind no-one has to the physical.




The mind-body problem concerns the relationship between these two sets
of properties. The mind-body problem breaks down into a number of
components.


1. The ontological question: what are mental states and what are
physical states? Is one class a subclass of the other, so that all
mental states are physical, or vice versa? Or are mental states and
physical states entirely distinct?
2. The causal question: do physical states influence mental states?
Do mental states influence physical states? If so, how?




Different aspects of the mind-body problem arise for different aspects
of the mental, such as consciousness, intentionality, the self.


3. The problem of consciousness: what is consciousness? How is it
related to the brain and the body?
4. The problem of intentionality: what is intentionality? How is it
related to the brain and the body?
5. The problem of the self: what is the self? How is it related to
the brain and the body?




Other aspects of the mind-body problem arise for aspects of the
physical. For example:


6. The problem of embodiment: what is it for the mind to be housed in
a body? What is it for a body to belong to a particular subject?




The seemingly intractable nature of these problems have given rise to
many different philosophical views.




Materialist views say that, despite appearances to the contrary,
mental states are just physical states. Behaviourism, functionalism,
mind-brain identity theory and the computational theory of mind are
examples of how materialists attempt to explain how this can be
so. The most common factor in such theories is the attempt to
explicate the nature of mind and consciousness in terms of their
ability to directly or indirectly modify behaviour, but there are
versions of materialism that try to tie the mental to the physical
without explicitly explaining the mental in terms of its
behaviour-modifying role. The latter are often grouped together under
the label 'non-reductive physicalism', though this label
is itself rendered elusive because of the controversial nature of the
term 'reduction'.




Idealist views say that physical states are really mental. This is
because the physical world is an *empirical* world and, as
such, it is the intersubjective product of our collective
experience.




Dualist views (the subject of this entry) say that the mental and the
physical are both real and neither can be assimilated to the
other. For the various forms that dualism can take and the associated
problems, see below.




In sum, we can say that there is a mind-body problem because both
consciousness and thought, broadly construed, seem very different from
anything physical and there is no convincing consensus on how to build
a satisfactorily unified picture of creatures possessed of both a mind
and a body.




Other entries which concern aspects of the mind-body problem include
(among many others):
 behaviorism, 
 consciousness, 
 eliminative materialism, 
 epiphenomenalism, 
 functionalism, 
 identity theory,
 intentionality, 
 mental causation, 
 neutral monism, 
and
 physicalism.



### 1.2 History of dualism


In dualism, 'mind' is contrasted with
'body', but at different times, different aspects of the
mind have been the centre of attention. In the classical and mediaeval
periods, it was the intellect that was thought to be most obviously
resistant to a materialistic account: from Descartes on, the main
stumbling block to materialist monism was supposed to be
'consciousness', of which phenomenal consciousness or
sensation came to be considered as the paradigm instance.




The classical emphasis originates in Plato's *Phaedo*. Plato
believed that the true substances are not physical bodies, which are
ephemeral, but the eternal Forms of which bodies are imperfect copies.
These Forms not only make the world possible, they also make it
intelligible, because they perform the role of universals, or what
Frege called 'concepts'. It is their connection with
intelligibility that is relevant to the philosophy of mind. Because
Forms are the grounds of intelligibility, they are what the intellect
must grasp in the process of understanding. In *Phaedo* Plato
presents a variety of arguments for the immortality of the soul, but
the one that is relevant for our purposes is that the intellect is
immaterial because Forms are immaterial and intellect must have an
affinity with the Forms it apprehends (78b4-84b8). This affinity
is so strong that the soul strives to leave the body in which it is
imprisoned and to dwell in the realm of Forms. It may take many
reincarnations before this is achieved. Plato's dualism is not,
therefore, simply a doctrine in the philosophy of mind, but an
integral part of his whole metaphysics.




One problem with Plato's dualism was that, though he speaks of the
soul as imprisoned in the body, there is no clear account of what
binds a particular soul to a particular body. Their difference in
nature makes the union a mystery.




Aristotle did not believe in Platonic Forms, existing independently of
their instances. Aristotelian forms (the capital 'F' has
disappeared with their standing as autonomous entities) are the
natures and properties of things and exist embodied in those
things. This enabled Aristotle to explain the union of body and soul
by saying that the soul is the form of the body. This means that a
particular person's soul is no more than his nature as a human
being. Because this seems to make the soul into a property of the
body, it led many interpreters, both ancient and modern, to interpret
his theory as materialistic. The interpretation of Aristotle's
philosophy of mind - and, indeed, of his whole doctrine of
form - remains as live an issue today as it was immediately after
his death (Robinson 1983 and 1991; Nussbaum 1984; Rorty and Nussbaum,
eds, 1992). Nevertheless, the text makes it clear that Aristotle
believed that the intellect, though part of the soul, differs from
other faculties in not having a bodily organ. His argument for this
constitutes a more tightly argued case than Plato's for the
immateriality of thought and, hence, for a kind of dualism. He argued
that the intellect must be immaterial because if it were material it
could not receive all forms. Just as the eye, because of its
particular physical nature, is sensitive to light but not to sound,
and the ear to sound and not to light, so, if the intellect were in a
physical organ it could be sensitive only to a restricted range of
physical things; but this is not the case, for we can think about any
kind of material object (*De Anima* III,4; 429a10-b9). As
it does not have a material organ, its activity must be essentially
immaterial.




It is common for modern Aristotelians, who otherwise have a high view
of Aristotle's relevance to modern philosophy, to treat this argument
as being of purely historical interest, and not essential to
Aristotle's system as a whole. They emphasize that he was not a
'Cartesian' dualist, because the intellect is an aspect of
the soul and the soul is the form of the body, not a separate
substance. Kenny (1989) argues that Aristotle's theory of mind as form
gives him an account similar to Ryle (1949), for it makes the soul
equivalent to the dispositions possessed by a living body. This
'anti-Cartesian' approach to Aristotle arguably ignores
the fact that, for Aristotle, the form *is* the substance.




These issues might seem to be of purely historical interest. But we
shall see in below, in section 4.5, that this is not so.




The identification of form and substance is a feature of Aristotle's
system that Aquinas effectively exploits in this context, identifying
soul, intellect and form, and treating them as a substance. (See, for
example, Aquinas (1912), Part I, questions 75 and 76.) But though the
form (and, hence, the intellect with which it is identical) are the
substance of the human person, they are not the person itself. Aquinas
says that when one addresses prayers to a saint - other than the
Blessed Virgin Mary, who is believed to retain her body in heaven and
is, therefore, always a complete person - one should say, not, for
example, 'Saint Peter pray for us', but 'soul of Saint
Peter pray for us'. The soul, though an immaterial substance, is the
person only when united with its body. Without the body, those aspects
of its personal memory that depend on images (which are held to be
corporeal) will be lost.(See Aquinas (1912), Part I, question 89.)




The more modern versions of dualism have their origin in Descartes'
*Meditations*, and in the debate that was consequent upon
Descartes' theory. Descartes was a *substance dualist*. He
believed that there were two kinds of substance: matter, of which the
essential property is that it is spatially extended; and mind, of
which the essential property is that it thinks. Descartes' conception
of the relation between mind and body was quite different from that
held in the Aristotelian tradition. For Aristotle, there is no exact
science of matter. How matter behaves is essentially affected by the
form that is in it. You cannot combine just any matter with any 
form - you cannot make a knife out of butter, nor a human being out
of paper - so the nature of the matter is a necessary condition
for the nature of the substance. But the nature of the substance does
not follow from the nature of its matter alone: there is no
'bottom up' account of substances. Matter is a
determinable made determinate by form. This was how Aristotle thought
that he was able to explain the connection of soul to body: a
particular soul exists as the organizing principle in a particular
parcel of matter.




The belief in the relative indeterminacy of matter is one reason for
Aristotle's rejection of atomism. If matter is atomic, then it is
already a collection of determinate objects in its own right, and it
becomes natural to regard the properties of macroscopic substances as
mere summations of the natures of the atoms.




Although, unlike most of his fashionable contemporaries and immediate
successors, Descartes was not an atomist, he was, like the others, a
mechanist about the properties of matter. Bodies are machines that
work according to their own laws. Except where there are minds
interfering with it, matter proceeds deterministically, in its own
right. Where there are minds requiring to influence bodies, they must
work by 'pulling levers' in a piece of machinery that already
has its own laws of operation. This raises the question of where those
'levers' are in the body. Descartes opted for the pineal gland,
mainly because it is not duplicated on both sides of the brain, so it
is a candidate for having a unique, unifying function.




The main uncertainty that faced Descartes and his contemporaries,
however, was not *where* interaction took place, but
*how* two things so different as thought and extension could
interact at all. This would be particularly mysterious if one had an
*impact* view of causal interaction, as would anyone influenced
by atomism, for whom the paradigm of causation is like two billiard
balls cannoning off one another.




Various of Descartes' disciples, such as Arnold Geulincx and Nicholas
Malebranche, concluded that all mind-body interactions required the
direct intervention of God. The appropriate states of mind and body
were only the *occasions* for such intervention, not real
causes. Now it would be convenient to think that occasionalists held
that all causation was natural *except* for that between mind
and body. In fact they generalized their conclusion and treated all
causation as directly dependent on God. Why this was so, we cannot
discuss here.




Descartes' conception of a dualism of *substances* came under
attack from the more radical empiricists, who found it difficult to
attach sense to the concept of substance at all. Locke, as a moderate
empiricist, accepted that there were both material and immaterial
substances. Berkeley famously rejected material substance, because he
rejected all existence outside the mind. In his early
*Notebooks*, he toyed with the idea of rejecting immaterial
substance, because we could have no idea of it, and reducing the self
to a collection of the 'ideas' that constituted its contents. Finally,
he decided that the self, conceived as something over and above the
ideas of which it was aware, was essential for an adequate
understanding of the human person. Although the self and its acts are
not presented to consciousness as *objects* of awareness, we are
obliquely aware of them simply by dint of being active subjects. Hume
rejected such claims, and proclaimed the self to be nothing more than a
concatenation of its ephemeral contents.




In fact, Hume criticised the whole conception of substance for
lacking in empirical content: when you search for the owner of the
properties that make up a substance, you find nothing but further
properties. Consequently, the mind is, he claimed, nothing but a
'bundle' or 'heap' of impressions and 
ideas - that is, of particular mental states or events, without an
owner. This position has been labelled *bundle dualism*, and it
is a special case of a general *bundle theory of substance*,
according to which objects in general are just organised collections of
properties. The problem for the Humean is to explain what binds the
elements in the bundle together. This is an issue for any kind of
substance, but for material bodies the solution seems fairly
straightforward: the unity of a physical bundle is constituted by some
form of causal interaction between the elements in the bundle. For the
mind, mere causal connection is not enough; some further relation of
co-consciousness is required. We shall see in 5.2.1 that it is
problematic whether one can treat such a relation as more primitive
than the notion of belonging to a subject.




One should note the following about Hume's theory. His bundle theory
is a theory about the nature of the unity of the mind. As a theory
about this unity, it is not necessarily dualist. Parfit (1970, 1984)
and Shoemaker (1984, ch. 2), for example, accept it as physicalists. In
general, physicalists will accept it unless they wish to ascribe the
unity to the brain or the organism as a whole. Before the bundle theory
can be dualist one must accept *property* dualism, for more
about which, see the next section.




A crisis in the history of dualism came, however, with the growing
popularity of *mechanism* in science in the nineteenth century.
According to the mechanist, the world is, as it would now be expressed,
'closed under physics'. This means that everything that
happens follows from and is in accord with the laws of physics. There
is, therefore, no scope for interference in the physical world by the
mind in the way that interactionism seems to require. According to the
mechanist, the conscious mind is an *epiphenomenon* (a notion
given general currency by T. H. Huxley 1893): that is, it is a
by-product of the physical system which has no influence back on it. In
this way, the facts of consciousness are acknowledged but the integrity
of physical science is preserved. However, many philosophers found it
implausible to claim such things as the following; the pain that I have
when you hit me, the visual sensations I have when I see the ferocious
lion bearing down on me or the conscious sense of understanding I have
when I hear your argument - all have nothing directly to do with
the way I respond. It is very largely due to the need to avoid this
counterintuitiveness that we owe the concern of twentieth century
philosophy to devise a plausible form of materialist monism. But,
although dualism has been out of fashion in psychology since the advent
of behaviourism (Watson 1913) and in philosophy since Ryle (1949),
the argument is by no means over. Some distinguished neurologists, such
as Sherrington (1940) and Eccles (Popper and Eccles 1977) have
continued to defend dualism as the only theory that can preserve the
data of consciousness. Amongst mainstream philosophers, discontent with
physicalism led to a modest revival of property dualism in the last
decade of the twentieth century. At least some of the reasons for this
should become clear below.


## 2. Varieties of Dualism: Ontology




There are various ways of dividing up kinds of dualism. One natural
way is in terms of what sorts of things one chooses to be dualistic
about. The most common categories lighted upon for these purposes are
*substance* and *property*, giving one *substance
dualism* and *property dualism*. There is, however, an
important third category, namely *predicate dualism*. As this
last is the weakest theory, in the sense that it claims least, I shall
begin by characterizing it.


### 2.1 Predicate dualism




Predicate dualism is the theory that psychological or mentalistic
predicates are (a) essential for a full description of the world and
(b) are not reducible to physicalistic predicates. For a mental
predicate to be reducible, there would be bridging laws connecting
types of psychological states to types of physical ones in such a way
that the use of the mental predicate carried no information that could
not be expressed without it. An example of what we believe to be a
true type reduction outside psychology is the case of water, where
water is always H2O: something is water if and only if it
is H2O. If one were to replace the word 'water'
by 'H2O', it is plausible to say that one could
convey all the same information. But the terms in many of the special
sciences (that is, any science except physics itself) are not
reducible in this way. Not every *hurricane* or every
*infectious disease*, let alone every *devaluation of the
currency* or every *coup d'etat* has the same constitutive
structure. These states are defined more by *what they do* than
by their *composition or structure.* Their names are classified
as *functional terms* rather than *natural kind
terms*. It goes with this that such kinds of state are
*multiply realizable*; that is, they may be constituted by
different kinds of physical structures under different
circumstances. Because of this, unlike in the case of water and
H2O, one could not replace these terms by some more basic
physical description and still convey the same information. There is
no particular description, using the language of physics or chemistry,
that would do the work of the word 'hurricane', in the way
that 'H2O' would do the work of
'water'. It is widely agreed that many, if not all,
psychological states are similarly irreducible, and so psychological
predicates are not reducible to physical descriptions and one has
predicate dualism. (The classic source for irreducibility in the
special sciences in general is Fodor (1974), and for irreducibility in
the philosophy of mind, Davidson (1971).)


### 2.2 Property Dualism




Whereas predicate dualism says that there are two essentially
different kinds of *predicates* in our *language*,
property dualism says that there are two essentially different kinds of
*property* out in the world. Property dualism can be seen as a
step stronger than predicate dualism. Although the predicate
'hurricane' is not equivalent to any single description
using the language of physics, we believe that each individual
hurricane is *nothing but* a collection of physical atoms
behaving in a certain way: one need have no more than the physical
atoms, with their normal physical properties, following normal physical
laws, for there to be a hurricane. One might say that we need more than
the *language* of physics to describe and explain the weather,
but we do not need more than its *ontology*. There is *token
identity* between each individual hurricane and a mass of atoms,
even if there is no *type identity* between hurricanes as kinds
and some particular structure of atoms as a kind. Genuine property
dualism occurs when, even at the individual level, the ontology of
physics is not sufficient to constitute what is there. The irreducible
language is not just another way of describing what there is, it
requires that there be something more there than was allowed for in the
initial ontology. Until the early part of the twentieth century, it was
common to think that biological phenomena ('life') required
property dualism (an irreducible 'vital force'), but nowadays the
special physical sciences other than psychology are generally thought
to involve only predicate dualism. In the case of mind, property
dualism is defended by those who argue that the qualitative nature of
consciousness is not merely another way of categorizing states of the
brain or of behaviour, but a genuinely emergent phenomenon.


### 2.3 Substance Dualism




There are two important concepts deployed in this notion. One is
that of *substance*, the other is the *dualism* of these
substances. A substance is characterized by its properties, but,
according to those who believe in substances, it is more than the
collection of the properties it possesses, it is *the thing
which* possesses them. So the mind is not just a collection of
thoughts, but is *that which* thinks, an immaterial substance
over and above its immaterial states. Properties are the properties of
*objects*. If one is a property dualist, one may wonder what
kinds of objects possess the irreducible or immaterial properties in
which one believes. One can use a neutral expression and attribute them
to *persons*, but, until one has an account of *person*,
this is not explanatory. One might attribute them to human beings
*qua* animals, or to the brains of these animals. Then one will
be holding that these immaterial properties are possessed by what is
otherwise a purely material thing. But one may also think that not only
mental states are immaterial, but that the subject that possesses them
must also be immaterial. Then one will be a dualist about *that to
which mental states and properties belong* as well about the
properties themselves. Now one might try to think of these subjects as
just bundles of the immaterial states. This is Hume's view. But if one
thinks that the owner of these states is something quite over and above
the states themselves, and is immaterial, as they are, one will be a
*substance dualist*.




Substance dualism is also often dubbed 'Cartesian
dualism', but some substance dualists are keen to distinguish
their theories from Descartes's. E. J. Lowe, for example, is a
substance dualist, in the following sense. He holds that a normal
human being involves two substances, one a body and the other a
person. The latter is not, however, a purely mental substance that can
be defined in terms of thought or consciousness alone, as Descartes
claimed. But persons and their bodies have different identity
conditions and are both substances, so there are two substances
essentially involved in a human being, hence this is a form of
substance dualism. Lowe (2006) claims that his theory is close to
P. F. Strawson's (1959), whilst admitting that Strawson would not have
called it substance dualism.


## 3. Varieties of Dualism: Interaction




If mind and body are different realms, in the way required by either
property or substance dualism, then there arises the question of how
they are related. Common sense tells us that they interact: thoughts
and feelings are at least sometimes caused by bodily events and at
least sometimes themselves give rise to bodily responses. I shall now
consider briefly the problems for interactionism, and its main rivals,
epiphenomenalism and parallelism.


### 3.1 Interactionism




Interactionism is the view that mind and body - or mental
events and physical events - causally influence each other. That
this is so is one of our common-sense beliefs, because it appears to be
a feature of everyday experience. The physical world influences my
experience through my senses, and I often react behaviourally to those
experiences. My thinking, too, influences my speech and my actions.
There is, therefore, a massive natural prejudice in favour of
interactionism. It has been claimed, however, that it faces serious
problems (some of which were anticipated in section 1).




The simplest objection to interaction is that, in so far as mental
properties, states or substances are of radically different kinds from
each other, they lack that communality necessary for interaction. It is
generally agreed that, in its most naive form, this objection to
interactionism rests on a 'billiard ball' picture of
causation: if all causation is by impact, how can the material and the
immaterial impact upon each other? But if causation is either by a more
ethereal force or energy or only a matter of constant conjunction,
there would appear to be no problem in principle with the idea of
interaction of mind and body.




Even if there is no objection in principle, there appears to be a
conflict between interactionism and some basic principles of physical
science. For example, if causal power was flowing in and out of the
physical system, energy would not be conserved, and the conservation
of energy is a fundamental scientific law. Various responses have been
made to this. One suggestion is that it might be possible for mind to
influence the *distribution* of energy, without altering its
quantity. (See Averill and Keating 1981). Another response is to
challenge the relevance of the conservation principle in this context.
The conservation principle states that 'in a causally isolated
system the total amount of energy will remain constant'. Whereas
'[t]he interactionist denies...that the human body is an
isolated system', so the principle is irrelevant (Larmer (1986),
282: this article presents a good brief survey of the options). This
approach has been termed *conditionality*, namely the view that
conservation is conditional on the physical system being closed, that
is, that nothing non-physical is interacting or interfering with it,
and, of course, the interactionist claims that this condition is,
trivially, not met. That conditionality is the best line for the
dualist to take, and that other approaches do not work, is defended in
Pitts (2019) and Cucu and Pitts (2019). This, they claim, makes the
plausibility of interactionism an empirical matter which only close
investigation on the fine operation of the brain could hope to
settle. Cucu, in a separate article (2018), claims to find critical
neuronal events which do not have sufficient physical explanation.This
claim clearly needs further investigation.




Robins Collins (2011) has claimed that the appeal to conservation by
opponents of interactionism is something of a red herring because
conservation principles are not ubiquitous in physics. He argues that
energy is not conserved in general relativity, in quantum theory, or
in the universe taken as a whole. Why then, should we insist on it in
mind-brain interaction?




Most discussion of interactionism takes place in the context of the
assumption that it is incompatible with the world's being 'closed
under physics'. This is a very natural assumption, but it is not
justified if causal overdetermination of behaviour is possible. There
could then be a complete physical cause of behaviour, and a mental one.
The strongest intuitive objection against overdetermination is clearly
stated by Mills (1996: 112), who is himself a defender of
overdetermination.




For *X* to be a cause of *Y*, *X* must contribute
something to *Y*. The only way a purely mental event could
contribute to a purely physical one would be to contribute some
feature not already determined by a purely physical event. But if
physical closure is true, there is no feature of the purely physical
effect that is not contributed by the purely physical cause. Hence
interactionism violates physical closure after all.




Mills says that this argument is invalid, because a physical event
can have features not explained by the event which is its sufficient
cause. For example, "the rock's hitting the window is causally
sufficient for the window's breaking, and the window's breaking has the
feature of being the third window-breaking in the house this year; but
the facts about prior window-breakings, rather than the rock's hitting
the window, are what cause this window-breaking to have this
feature."




The opponent of overdetermination could perhaps reply that his
principle applies, not to every feature of events, but to a 
subgroup - say, intrinsic features, not merely relational or comparative
ones. It is this kind of feature that the mental event would have to
cause, but physical closure leaves no room for this. These matters are
still controversial.




The problem with closure of physics may be radically altered if
physical laws are indeterministic, as quantum theory seems to assert.
If physical laws are deterministic, then any interference from outside
would lead to a breach of those laws. But if they are indeterministic,
might not interference produce a result that has a probability greater
than zero, and so be consistent with the laws? This way, one might have
interaction yet preserve a kind of nomological closure, in the sense
that no laws are infringed. Because it involves assessing the
significance and consequences of quantum theory, this is a difficult
matter for the non-physicist to assess. Some argue that indeterminacy
manifests itself only on the subatomic level, being cancelled out by
the time one reaches even very tiny macroscopic objects: and human
behaviour is a macroscopic phenomenon. Others argue that the structure
of the brain is so finely tuned that minute variations could have
macroscopic effects, rather in the way that, according to 'chaos
theory', the flapping of a butterfly's wings in China might affect the
weather in New York. (For discussion of this, see Eccles (1980),
(1987), and Popper and Eccles (1977).) Still others argue that quantum
indeterminacy manifests itself directly at a high level, when acts of
observation collapse the wave function, suggesting that the mind may
play a direct role in affecting the state of the world (Hodgson
1988; Stapp 1993).


### 3.2 Epiphenomenalism




If the reality of property dualism is not to be denied, but the
problem of how the immaterial is to affect the material is to be
avoided, then epiphenomenalism may seem to be the answer. According to
this theory, mental events are caused by physical events, but have no
causal influence on the physical. I have introduced this theory as if
its point were to avoid the problem of how two different categories of
thing might interact. In fact, it is, at best, an incomplete solution
to this problem. If it is mysterious how the non-physical can have it
in its nature to influence the physical, it ought to be equally
mysterious how the physical can have it in its nature to produce
something non-physical. But that this latter is what occurs is an
essential claim of epiphenomenalism. (For development of this point,
see Green (2003), 149-51). In fact, epiphenomenalism is more effective
as a way of saving the autonomy of the physical (the world as
'closed under physics') than as a contribution to avoiding the
need for the physical and non-physical to have causal commerce.




There are at least three serious problems for epiphenomenalism.
First, as I indicated in *section 1*, it is profoundly
counterintuitive. What could be more apparent than that it is the pain
that I feel that makes me cry, or the visual experience of the boulder
rolling towards me that makes me run away? At least one can say that
epiphenomenalism is a fall-back position: it tends to be adopted
because other options are held to be unacceptable.




The second problem is that, if mental states do nothing, there is no
reason why they should have evolved. This objection ties in with the
first: the intuition there was that conscious states clearly modify our
behaviour in certain ways, such as avoiding danger, and it is plain
that they are very useful from an evolutionary perspective.




Frank Jackson (1982) replies to this objection by saying that it is
the brain state associated with pain that evolves for this reason: the
sensation is a by-product. Evolution is full of useless or even harmful
by-products. For example, polar bears have evolved thick coats to keep
them warm, even though this has the damaging side effect that they are
heavy to carry. Jackson's point is true in general, but does not seem
to apply very happily to the case of mind. The heaviness of the polar
bear's coat follows directly from those properties and laws which make
it warm: one could not, in any simple way, have one without the other.
But with mental states, dualistically conceived, the situation is quite
the opposite. The laws of physical nature which, the mechanist says,
make brain states cause behaviour, in no way explain why brain states
should give rise to conscious ones. The laws linking mind and brain are
what Feigl (1958) calls *nomological danglers*, that is, brute
facts added onto the body of integrated physical law. Why there should
have been by-products of *that* kind seems to have no
evolutionary explanation.




The third problem concerns the rationality of belief in
epiphenomenalism, *via* its effect on the problem of other
minds. It is natural to say that I know that I have mental states
because I experience them directly. But how can I justify my belief
that others have them? The simple version of the 'argument from
analogy' says that I can extrapolate from my own case. I know
that certain of my mental states are correlated with certain pieces of
behaviour, and so I infer that similar behaviour in others is also
accompanied by similar mental states. Many hold that this is a weak
argument because it is induction from one instance, namely, my own. The
argument is stronger if it is not a simple induction but an
'argument to the best explanation'. I seem to know from my
own case that mental events can be the explanation of behaviour, and I
know of no other candidate explanation for typical human behaviour, so
I postulate the same explanation for the behaviour of others. But if
epiphenomenalism is true, my mental states do not explain my behaviour
and there is a physical explanation for the behaviour of others. It is
explanatorily redundant to postulate such states for others. I know, by
introspection, that I have them, but is it not just as likely that I
alone am subject to this quirk of nature, rather than that everyone
is?



For more detailed treatment and further reading on this topic, see the
entry
 epiphenomenalism.
 

### 3.3 Parallelism




The epiphenomenalist wishes to preserve the integrity of physical
science and the physical world, and appends those mental features that
he cannot reduce. The parallelist preserves both realms intact, but
denies all causal interaction between them. They run in harmony with
each other, but not because their mutual influence keeps each other in
line. That they should behave *as if* they were interacting
would seem to be a bizarre coincidence. This is why parallelism has
tended to be adopted only by those - like Leibniz - who
believe in a pre-established harmony, set in place by God. The
progression of thought can be seen as follows. Descartes believes in a
more or less natural form of interaction between immaterial mind and
material body. Malebranche thought that this was impossible naturally,
and so required God to intervene specifically on each occasion on which
interaction was required. Leibniz decided that God might as well set
things up so that they always behaved *as if* they were
interacting, without particular intervention being required. Outside
such a theistic framework, the theory is incredible. Even within such a
framework, one might well sympathise with Berkeley's instinct that once
genuine interaction is ruled out one is best advised to allow that God
creates the physical world directly, within the mental realm itself, as
a construct out of experience.


## 4. Arguments for Dualism


### 4.1 The Knowledge Argument Against Physicalism




One category of arguments for dualism is constituted by the standard
objections against physicalism. Prime examples are those based on the
existence of qualia, the most important of which is the so-called
'knowledge argument'. Because this argument has its own
entry (see the entry
 qualia: the knowledge argument),
 I shall deal relatively briefly with it here. One should bear in
mind, however, that all arguments against physicalism are also
arguments for the irreducible and hence immaterial nature of the mind
and, given the existence of the material world, are thus arguments
for dualism.




The knowledge argument asks us to imagine a future scientist who has
lacked a certain sensory modality from birth, but who has acquired a
perfect scientific understanding of how this modality operates in
others. This scientist - call him Harpo - may have been
born stone deaf, but become the world's greatest expert on the
machinery of hearing: he knows everything that there is to know within
the range of the physical and behavioural sciences about hearing.
Suppose that Harpo, thanks to developments in neurosurgery, has an
operation which finally enables him to hear. It is suggested that he
will then learn something he did not know before, which can be
expressed as *what it is like to hear*, or the
*qualitative* or *phenomenal nature of sound*. These
qualitative features of experience are generally referred to as
*qualia*. If Harpo learns something new, he did not know
everything before. He knew all the physical facts before. So what he
learns on coming to hear - the facts about the nature of
experience or the nature of qualia - are non-physical. This
establishes at least a state or property dualism. (See Jackson 1982;
Robinson 1982.)




There are at least two lines of response to this popular but
controversial argument. First is the 'ability' response.
According to this, Harpo does not acquire any new factual knowledge,
only 'knowledge how', in the form of the ability to respond
directly to sounds, which he could not do before. This essentially
behaviouristic account is exactly what the intuition behind the
argument is meant to overthrow. Putting ourselves in Harpo's position,
it is meant to be obvious that what he acquires is knowledge of what
something is *like*, not just *how to do* something. Such
appeals to intuition are always, of course, open to denial by those who
claim not to share the intuition. Some ability theorists seem to blur
the distinction between knowing what something is like and knowing how
to do something, by saying that the ability Harpo acquires is to
*imagine* or *remember* the nature of sound. In this
case, what he acquires the ability to *do* involves the
representation to himself of what the thing is *like*. But this
conception of representing to oneself, especially in the form of
imagination, seems sufficiently close to producing in oneself something
very like a sensory experience that it only defers the problem: until
one has a physicalist gloss on what constitutes such representations as
those involved in conscious memory and imagination, no progress has
been made.




The other line of response is to argue that, although Harpo's new
knowledge is factual, it is not knowledge of a new fact. Rather, it is
new way of grasping something that he already knew. He does not realise
this, because the concepts employed to capture experience (such as
'looks red' or 'sounds C-sharp') are similar to
demonstratives, and demonstrative concepts lack the kind of descriptive
content that allow one to infer what they express from other pieces of
information that one may already possess. A total scientific knowledge
of the world would not enable you to say which time was
'now' or which place was 'here'. Demonstrative
concepts pick something out without saying anything extra about it.
Similarly, the scientific knowledge that Harpo originally possessed did
not enable him to anticipate what it would be like to re-express some
parts of that knowledge using the demonstrative concepts that only
experience can give one. The knowledge, therefore, appears to be
genuinely new, whereas only the mode of conceiving it is novel.




Proponents of the epistemic argument respond that it is problematic
to maintain both that the qualitative nature of experience can be
genuinely novel, and that the quality itself be the same as some
property already grasped scientifically: does not the experience's
phenomenal nature, which the demonstrative concepts capture, constitute
a property in its own right? Another way to put this is to say that
phenomenal concepts are not pure demonstratives, like
'here' and 'now', or 'this' and
'that', because they do capture a genuine qualitative
content. Furthermore, experiencing does not seem to consist simply in
exercising a particular kind of concept, demonstrative or not. When
Harpo has his new form of experience, he does not simply exercise a new
concept; he also grasps something new - the phenomenal 
quality - with that concept. How decisive these considerations are,
remains controversial.


### 4.2 The Argument from Predicate Dualism to Property Dualism




I said above that predicate dualism might seem to have no
ontological consequences, because it is concerned only with the
different way things can be described within the contexts of the
different sciences, not with any real difference in the things
themselves. This, however, can be disputed.




The argument from predicate to property dualism moves in two steps,
both controversial. The first claims that the irreducible special
sciences, which are the sources of irreducible predicates, are not
wholly objective in the way that physics is, but depend for their
subject matter upon interest-relative perspectives on the world. This
means that they, and the predicates special to them, depend on the
existence of minds and mental states, for only minds have
interest-relative perspectives. The second claim is that 
psychology - the science of the mental - is itself an irreducible
special science, and so it, too, presupposes the existence of the
mental. Mental predicates therefore presuppose the mentality that
creates them: mentality cannot consist simply in the applicability of
the predicates themselves.




First, let us consider the claim that the special sciences are not
fully objective, but are interest-relative.




No-one would deny, of course, that the very same subject matter or
'hunk of reality' can be described in irreducibly different
ways and it still be just that subject matter or piece of reality. A
mass of matter could be characterized as a hurricane, or as a
collection of chemical elements, or as mass of sub-atomic particles,
and there be only the one mass of matter. But such different
explanatory frameworks seem to presuppose different perspectives on
that subject matter.




This is where basic physics, and perhaps those sciences reducible to
basic physics, differ from irreducible special sciences. On a realist
construal, the completed physics cuts physical reality up at its
ultimate joints: any special science which is nomically strictly
reducible to physics also, in virtue of this reduction, it could be
argued, cuts reality at its joints, but not at its minutest ones. If
scientific realism is true, a completed physics will tell one how the
world is, independently of any special interest or concern: it is just
*how the world is*. It would seem that, by contrast, a science
which is not nomically reducible to physics does not take its
legitimation from the underlying reality in this direct way. Rather,
such a science is formed from the collaboration between, on the one
hand, objective similarities in the world and, on the other,
perspectives and interests of those who devise the science. The concept
of hurricane is brought to bear from the perspective of creatures
concerned about the weather. Creatures totally indifferent to the
weather would have no reason to take the real patterns of phenomena
that hurricanes share as constituting a single kind of thing. With the
irreducible special sciences, there is an issue of *salience* ,
which involves a subjective component: a *selection* of
phenomena with a certain *teleology* in mind is required before
their structures or patterns are reified. The entities of metereology
or biology are, in this respect, rather like *Gestalt*
phenomena.




Even accepting this, why might it be thought that the
perspectivality of the special sciences leads to a genuine property
dualism in the philosophy of mind? It might seem to do so for the
following reason. Having a perspective on the world, perceptual or
intellectual, is a psychological state. So the irreducible special
sciences presuppose the existence of mind. If one is to avoid an
ontological dualism, the mind that has this perspective must be part of
the physical reality on which it has its perspective. But psychology,
it seems to be almost universally agreed, is one of those special
sciences that is not reducible to physics, so if its subject matter is
to be physical, it itself presupposes a perspective and, hence, the
existence of a mind to *see matter as* psychological. If this
mind is physical and irreducible, it presupposes mind to see it as
such. We seem to be in a vicious circle or regress.




We can now understand the motivation for full-blown reduction. A
true basic physics represents the world as it is in itself, and if the
special sciences were reducible, then the existence of their ontologies
would make sense as expressions of the physical, not just as ways of
seeing or interpreting it. They could be understood 'from the
bottom up', not from top down. The irreducibility of the special
sciences creates no problem for the dualist, who sees the explanatory
endeavor of the physical sciences as something carried on from a
perspective conceptually outside of the physical world. Nor need this
worry a physicalist, *if* he can reduce psychology, for then he
could understand 'from the bottom up' the acts (with their
internal, intentional contents) which created the irreducible
ontologies of the other sciences. But psychology is one of the least
likely of sciences to be reduced. If psychology cannot be reduced, this
line of reasoning leads to real emergence for mental acts and hence to
a real dualism for the properties those acts instantiate (Robinson
2003).


### 4.3 The Modal Argument




There is an argument, which has roots in Descartes (*Meditation
VI*), which is a modal argument for dualism. One might put it as
follows:


1. It is imaginable that one's mind might exist without one's body. 



therefore
2. It is conceivable that one's mind might exist without one's body. 



therefore
3. It is possible one's mind might exist without one's body. 



therefore
4. One's mind is a different entity from one's body.




The rationale of the argument is a move from imaginability to real
possibility. I include (2) because the notion of conceivability has one
foot in the psychological camp, like imaginability, and one in the camp
of pure logical possibility and therefore helps in the transition from
one to the other.




This argument should be distinguished from a similar
'conceivability' argument, often known as the 'zombie
hypothesis', which claims the imaginability and possibility of my
body (or, in some forms, a body physically just like it) existing
without there being any conscious states associated with it. (See, for
example, Chalmers (1996), 94-9.) This latter argument, if sound, would
show that conscious states were something over and above physical
states. It is a *different* argument because the hypothesis that
the unaltered body could exist without the mind is *not* the
same as the suggestion that the mind might continue to exist without
the body, nor are they trivially equivalent. The zombie argument
establishes only property dualism and a property dualist might think
disembodied existence inconceivable - for example, if he thought
the identity of a mind through time depended on its relation to a body
(e.g., Penelhum 1970).




Before Kripke (1972/80), the first challenge to such an argument
would have concerned the move from (3) to (4). When philosophers
generally believed in contingent identity, that move seemed to them
invalid. But nowadays that inference is generally accepted and the
issue concerns the relation between imaginability and possibility.
No-one would nowadays identify the two (except, perhaps, for certain
quasi-realists and anti-realists), but the view that imaginability is a
solid test for possibility has been strongly defended. W. D. Hart
((1994), 266), for example, argues that no clear example has been
produced such that "one can imagine that p (and tell less
imaginative folk a story that enables them to imagine that p) plus a
good argument that it is impossible that p. No such counterexamples
have been forthcoming..." This claim is at least contentious.
There seem to be good arguments that time-travel is incoherent, but
every episode of *Star-Trek* or *Doctor Who* shows how
one can imagine what it might be like were it possible.




It is worth relating the appeal to possibility in this argument to
that involved in the more modest, anti-physicalist, zombie argument.
The possibility of this hypothesis is also challenged, but all that is
necessary for a zombie to be possible is that all and only the things
that the physical sciences say about the body be true of such a
creature. As the concepts involved in such sciences - e.g.,
neuron, cell, muscle - seem to make no reference, explicit or
implicit, to their association with consciousness, and are defined in
purely physical terms in the relevant science texts, there is a very
powerful prima facie case for thinking that something could meet the
condition of being just like them and lack any connection with
consciousness. There is no parallel clear, uncontroversial and
regimented account of mental concepts as a whole that fails to invoke,
explicitly or implicitly, physical (e.g., behavioural) states.




For an analytical behaviourist the appeal to imaginability made in
the argument fails, not because imagination is not a reliable guide to
possibility, but because we cannot imagine such a thing, as it is a
priori impossible. The impossibility of disembodiment is rather like
that of time travel, because it is demonstrable a priori, though only
by arguments that are controversial. The argument can only get under
way for those philosophers who accept that the issue cannot be settled
a priori, so the possibility of the disembodiment that we can imagine
is still prima facie open.




A major rationale of those who think that imagination is not a safe
indication of possibility, even when such possibility is not eliminable
a priori, is that we can *imagine* that a posteriori necessities
might be false - for example, that Hesperus might not be
identical to Phosphorus. But if Kripke is correct, that is not a real
possibility. Another way of putting this point is that there are many
epistemic possibilities which are imaginable because they are epistemic
possibilities, but which are not real possibilities. Richard Swinburne
(1997, New Appendix C), whilst accepting this argument in general, has
interesting reasons for thinking that it cannot apply in the mind-body
case. He argues that in cases that involve a posteriori necessities,
such as those identities that need discovering, it is because we
identify those entities only by their 'stereotypes' (that
is, by their superficial features observable by the layman) that we can
be wrong about their essences. In the case of our experience of
ourselves this is not true.




Now it is true that the essence of Hesperus cannot be discovered by
a mere thought experiment. That is because what makes Hesperus Hesperus
is not the stereotype, but what underlies it. But it does not follow
that no one can ever have access to the essence of a substance, but
must always rely for identification on a fallible stereotype. One might
think that for the person him or herself, while what makes that person
that person underlies what is observable to others, it does not
underlie what is experienceable by that person, but is given directly in
their own self-awareness.




This is a very appealing Cartesian intuition: my identity as the
thinking thing that I am is revealed to me in consciousness, it is not
something beyond the veil of consciousness. Now it could be replied to
this that though I do access myself as a conscious subject, so
classifying myself is rather like considering myself *qua*
cyclist. Just as I might never have been a cyclist, I might never have
been conscious, if things had gone wrong in my very early life.
*I* am the organism, the animal, which might not have developed
to the point of consciousness, and that essence as animal is not
revealed to me just by introspection.




But there are vital differences between these cases. A cyclist is
explicitly presented as a *human being* (or creature of some
other animal species) cycling: there is no temptation to think of a
cyclist as a basic kind of thing in its own right. Consciousness is not
presented as a property of something, but as the subject itself.
Swinburne's claim that when we refer to ourselves we are referring to
something we think we are directly aware of and not to 'something
we know not what' that underlies our experience seemingly
'of ourselves' has powerful intuitive appeal and could only
be overthrown by very forceful arguments. Yet, even if we are not
referring primarily to a substrate, but to what is revealed in
consciousness, could it not still be the case that there is a necessity
stronger than causal connecting this consciousness to something
physical? To consider this further we must investigate what the limits
are of the possible analogy between cases of the water-H2O kind, and
the mind-body relation.




We start from the analogy between the water stereotype - how
water presents itself - and how consciousness is given
first-personally to the subject. It is plausible to claim that
something like water could exist without being H2O, but hardly that it
could exist without *some* underlying nature. There is, however,
no reason to deny that this underlying nature *could* be
homogenous with its manifest nature: that is, it would seem to be
possible that there is a world in which the water-like stuff is an
element, as the ancients thought, and is water-like all the way down.
The claim of the proponents of the dualist argument is that this latter
kind of situation can be known to be true a priori in the case of the
mind: that is, one can tell by introspection that it is not
more-than-causally dependent on something of a radically different
nature, such as a brain or body. What grounds might one have for
thinking that one could tell that a priori?




The only general argument that seem to be available for this would be
the principle that, for any two levels of discourse, *A* and
*B*, they are more-than-causally connected only if one entails
the other a priori. And the argument for accepting this principle
would be that the relatively uncontroversial cases of a posteriori
necessary connections are in fact cases in which one can argue a
priori from facts about the microstructure to the manifest facts. In
the case of water, for example, it would be claimed that it follows a
priori that *if* there were something with the properties
attributed to H2O by chemistry on a micro level, then that
thing would possess waterish properties on a macro level. What is
established a posteriori is that it is in fact H2O that
underlies and explains the waterish properties round here, not
something else: the sufficiency of the base - were it to 
obtain - to explain the phenomena, can be deduced a priori from the
supposed nature of the base. This is, in effect, the argument that
Chalmers uses to defend the zombie hypothesis. The suggestion is that
the whole category of a posteriori more-than-causally necessary
connections (often identified as a separate category of
*metaphysical necessity*) comes to no more than this. If we
accept that this is the correct account of a posteriori necessities,
and also deny the analytically reductionist theories that would be
necessary for a priori connections between mind and body, as
conceived, for example, by the behaviourist or the functionalist, does
it follow that we can tell a priori that consciousness is not
more-than-causally dependent on the body?




It is helpful in considering this question to employ a distinction
like Berkeley's between *ideas* and *notions*. Ideas are
the objects of our mental acts, and they capture 
transparently - 'by way of image or likeness' 
(*Principles*, sect. 27) - that of which they are the ideas. 
The self and its faculties
are not the *objects* of our mental acts, but are captured only
obliquely *in* the performance of its acts, and of these
Berkeley says we have *notions*, meaning by this that what we
capture of the nature of the dynamic agent does not seem to have the
same transparency as what we capture as the normal objects of the
agent's mental acts. It is not necessary to become involved in
Berkeley's metaphysics in general to feel the force of the claim that
the contents and internal objects of our mental acts are grasped with a
lucidity that exceeds that of our grasp of the agent and the acts
*per se*. Because of this, notions of the self perhaps have a
'thickness' and are permanently contestable: there seems
always to be room for more dispute as to what is involved in that
concept. (Though we shall see later, in 5.2.2, that there is a
'non-thick' way of taking the Berkeleyan concept of a
*notion*.)




Because 'thickness' always leaves room for dispute, this
is one of those cases in philosophy in which one is at the mercy of the
arguments philosophers happen to think up. The conceivability argument
creates a prima facie case for thinking that mind has no more than
causal ontological dependence on the body. Let us assume that one
rejects analytical (behaviourist or functionalist) accounts of mental
predicates. Then the above arguments show that any necessary dependence
of mind on body does not follow the model that applies in other
scientific cases. This does not show that there may not be other
reasons for believing in such dependence, for so many of the concepts
in the area are still contested. For example, it might be argued that
identity through time requires the kind of spatial existence that only
body can give: or that the causal continuity required by a stream of
consciousness cannot be a property of mere phenomena. All these might
be put forward as ways of filling out those aspects of our
understanding of the self that are only obliquely, not transparently,
presented in self-awareness. The dualist must respond to any claim as
it arises: the conceivability argument does not pre-empt them.


### 4.4 From property dualism to substance dualism




All the arguments so far in this section have been either arguments
for property dualism only, or neutral between property and substance
dualism. In this subsection, and in section 4.5 we will consider some
arguments that have been proposed in favour of substance dualism.The
ones in this section can be regarded as preliminaries to that in 4.5
and they centre on discontent with property dualism in its Humean
form. 




Hume is generally credited with devising what is known as the 'bundle'
theory of the self (*Treatise* Book I, Part IV, section VI),
according to which there are mental states, but no further subject or
substance which possesses them. He famously expresses his theory as
follows.



> ...when I enter most intimately into what I
> call *myself*, I always stumble on some particular perception or
> other, of heat or cold, light or shade,love or hatred, pain or
> pleasure. I can never catch *myself* at any time without a
> perception, and can never observe any thing but the
> perception.




Nevertheless, in the Appendix of the same work he expressed
dissatisfaction with this account. Somewhat surprisingly, it is not
very clear just what his worry was, but it is expressed as follows:



> In short there are two principles, which I cannot render
> consistent; nor is it in my power to renounce either of them,
> viz. *that all our distinct perceptions are distinct existences,*
> and *that the mind never perceives any real connection between
> distinct existences*.




Berkeley had entertained a similar theory to the one found in Hume's
main text in his *Philosophical Commentaries*, (Notebook A, paras
577-81), but later rejected it for the claim that we could have
a *notion*, though not an *idea* of the self. This
Berkeleian view is expressed in more modern terms by John Foster.



> A natural response to Hume would be to say that, even if
> we cannot detect ourselves apart from our perceptions (our conscious
> experiences)we can at least detect ourselves in them ... Surely I am
> aware of [my experience], so to speak, from the inside - not as
> something presented, but as something which I have or as the
> experiential state which I am in ... and this is equivalent to saying
> that I detect it by being aware of myself being visually aware. (1991:
> 215)




There is a clash of intuitions here between which it is difficult to
arbitrate. There is an argument that is meant to favour the need for a
subject, as claimed by Berkeley and Foster.


1. If the bundle theory were true, then it should be possible to
identify mental events independently of, or prior to, identifying the
person or mind to which they belong.
2. It is not possible to identify mental events in this way.


Therefore,


3. The bundle theory is false.




E. J. Lowe (1996) defends this argument and argues for (2) as follows.



> What is wrong with the [bundle] theory is that ... it
> presupposes, untenably,that an account of the identity conditions of
> psychological modes can be provided which need not rely on reference
> to persons. But it emerges that the identity of any psychological mode
> turns on the identity of the person that possesses it. What this
> implies is that psychological modes are essentially modes of persons,
> and correspondingly that persons can be conceived of as
> substances.




To say that, according to the bundle theory, the identity conditions
of individual mental states must be independent of the identity of the
person who possesses them, is to say that their identity is
independent of the bundle to which they belong. Hume certainly thought
something like this, for he thought that an impression might 'float
free' from the mind to which it belonged, but it is not obvious that a
bundle theorist is forced to adopt this position. Perhaps the identity
of a mental event is bound up with the complex to which it
belongs. That this is impossible certainly needs further argument.




Hume seems, however, in the main text to unconsciously make a
concession to the opposing view, namely the view that there must be
something more than the items in the bundle to make up a mind. He says:



> The mind is a kind of theatre where several perceptions
> successively make their appearance; pass, re-pass, glide away and
> mingle in an infinite variety of postures and situations.




Talk of the mind as a theatre is, of course, normally associated with
the Cartesian picture, and the invocation of any necessary medium,
arena or even a field hypostasize some kind of entity which binds the
different contents together and without which they would not be a
single mind. Modern Humeans - such as Parfit (1971; 1984) or Dainton
(2008) - replace the theatre with a co-consciousness relation. So the
bundle theorist is perhaps not as restricted as Hume thought. The
bundle consists of the objects of awareness *and the
co-consciousness relation (or relations) that hold between them*,
and I think that the modern bundle theorist would want to say that it
is the nexus of co-consciousness relations that constitutes our sense
of the subject and of the act of awareness of the object. This
involves abandoning the second of Hume's principles. *that the mind
can never perceive any connection between distinct existences*,
because the co-consciousness relation is something of which we are
aware. The Humean point then becomes that we mistake the nexus of
relations for a kind of entity, in a way similar to that in which,
Hume claims,we mistake the regular succession of similar impressions
for an entity called an enduring physical object. Whether this really
makes sense in the end is another matter. I think that it is dubious
whether it can accommodate the subject as *agent*, but it does
mean that simple introspection probably cannot refute a sophisticated
bundle theory in the way that Lowe and Foster want. Hume's original
position seems to make him deny that we have any 'sense of self' at
all, whilst the version that allows for our awareness of the
relatedness accommodates it, but explains how it can be an
illusion. The rejection of bundle dualism, therefore, requires more
than an appeal to our intuitive awareness of ourselves as subjects.We
will see in the next section how arguments that defend the simplicity
of the self attempt to undercut the bundle theory.


### 4.5 Arguments from Personal Identity




There is a long tradition, dating at least from Reid (1785),
for arguing that the identity of persons over time is not a matter of
convention or degree in the way that the identity of other (complex)
substances is and that this shows that the self is a different kind of
entity from any physical body. Criticism of these arguments and of the
intuitions on which they rest, running from Hume to Parfit (1970:
1984), have left us with an inconclusive clash of intuitions. The
argument under consideration and which, possibly, has its first
statement in Madell (1981), does not concern identity through time, but
the consequences for identity of certain counterfactuals concerning
origin. It can, perhaps, therefore, break the stalemate which faces the
debate over diachronic identity. The claim is that the broadly
conventionalist ways which are used to deal with problem cases through
time for both persons and material objects, and which can also be
employed in cases of counterfactuals concerning origin for bodies,
cannot be used for similar counterfactuals concerning persons or
minds.




Concerning ordinary physical objects, it is easy to imagine
counterfactual cases where questions of identity become problematic.
Take the example of a particular table. We can scale counterfactual
suggestions as follows:


1. This table might have been made of ice.
2. This table might have been made of a different sort of wood.
3. This table might have been made of 95% of the wood it was made of
and 5% of some other wood.




The first suggestion would normally be rejected as clearly false,
but there will come a point along the spectrum illustrated by (i) and
(iii) and towards (iii) where the question of whether the hypothesised
table would be the same as the one that actually exists have no obvious
answer. It seems that the question of whether it 'really'
is the same one has no clear meaning: it is of, say, 75% the same
matter and of 25% different matter; these are the only genuine facts in
the case; the question of numerical identity can be decided in any
convenient fashion, or left unresolved. There will thus be a penumbra
of counterfactual cases where the question of whether two things would
be the same is not a matter of fact.




Let us now apply this thought to conscious subjects. Suppose that a
given human individual had had origins different from those which he in
fact had such that whether that difference affected *who he was*
was not obvious to intuition. What would count as such a case might be
a matter of controversy, but there must be one. Perhaps it is unclear
whether, if there had been a counterpart to Jones' body from the same
egg but a different though genetically identical sperm from the same
father, the person there embodied would have been Jones. Some
philosophers might regard it as obvious that sameness of sperm is
essential to the identity of a human body and to personal identity. In
that case imagine a counterpart sperm in which some of the molecules in
the sperm are different; would that be the same sperm? If one pursues
the matter far enough there will be indeterminacy which will infect
that of the resulting body. There must therefore be some difference
such that neither natural language nor intuition tells us whether the
difference alters the identity of the human body; a point, that is,
where the question of whether we have the same body is not a matter of
fact.




How one is to describe these cases is, in some respects, a matter of
controversy. Some philosophers think one can talk of *vague
identity* or *partial identity*. Others think that such
expressions are nonsensical. There is no space to discuss this issue
here. It is enough to assume, however, that questions of how one is
allowed to use the concept of identity effect only the care with which
one should characterize these cases, not any substantive matter of
fact. There are cases of substantial overlap of constitution in which
*that* fact is the only bedrock fact in the case: there is no
further fact about whether they are 'really' the same
object. If there were, then there would have to be a
*haecceitas* or *thisness* belonging to and individuating
each complex physical object, and this I am assuming to be implausible
if not unintelligible. (More about the conditions under which
*haecceitas* can make sense will be found below.)




One might plausibly claim that no similar *overlap of
constitution* can be applied to the counterfactual identity of
minds. In Geoffrey Madell's (1981) words:



> But while my present body can thus have its partial
> counterpart in some possible world, my present consciousness cannot.
> Any present state of consciousness that I can imagine either is or is
> not mine. There is no question of degree here. (91)




Why is this so? Imagine the case where we are not sure whether it
would have been Jones' body - and, hence, Jones - that
would have been created by the slightly modified sperm and the same
egg. Can we say, as we would for an object with no consciousness, that
the story *something the same, something different* is the whole
story: that overlap of constitution is all there is to it? For the
Jones body as such, this approach would do as well as for any other
physical object. But suppose Jones, in reflective mood, asks himself
'if that had happened, would I have existed?' There are at
least three answers he might give to himself. (i) I either would or
would not, but I cannot tell. (ii) There is no fact of the matter
whether I would or would not have existed: it is just a mis-posed
question. (iii) In some ways, or to some degree, I would have, and in
some ways, or to some degree, I would not. The creature who would have
existed would have had a kind of overlap of psychic constitution with
me.




The third answer parallels the response we would give in the case of
bodies. But as an account of the subjective situation, it is arguable
that this makes no sense. Call the creature that would have emerged
from the slightly modified sperm, 'Jones2'. Is the overlap
suggestion that, just as, say 85% of Jones2's original body would have
been identical with Jones', about 85% of his psychic life would have
been Jones'? That it would have been *like* 
Jones' - indeed that Jones2 might have had a psychic life 100% like 
Jones' - makes perfect sense, but that he might have been to that
degree, the same psyche - that Jones '85% existed'
 - arguably makes no sense. Take the case in which Jones and Jones2
have *exactly* similar lives throughout: which 85% of the 100%
similar mental events do they share? Nor does it make sense to suggest
that Jones might have participated in the whole of Jones2's psychic
life, but in a rather ghostly *only 85% there* manner. Clearly,
the notion of overlap of numerically identical psychic parts cannot be
applied in the way that overlap of actual bodily part constitution
quite unproblematically can.




This might make one try the second answer. We can apply the
'overlap' answer to the Jones body, but the question of
whether the minds or subjects would have been the same, has no clear
sense. It is difficult to see why it does not. Suppose Jones found out
that he had originally been one of twins, in the sense that the zygote
from which he developed had divided, but that the other half had died
soon afterwards. He can entertain the thought that if it had been his
half that had died, he would never have existed as a conscious being,
though someone would whose life, both inner and outer, might have been
very similar to his. He might feel rather guiltily grateful that it was
the other half that died. It would be strange to think that Jones is
wrong to think that there is a matter of fact about this. And how is
one to 'manage' the transition from the case where there is
a matter of fact to the case where there is not?




If the reasoning above is correct, one is left with only the first
option. If so, there has to be an absolute matter of fact from the
subjective point of view. But the physical examples we have considered
show that when something is essentially complex, this cannot be the
case. When there is constitution, degree and overlap of constitution
are inevitably possible. So the mind must be simple, and this is
possible only if it is something like a Cartesian substance.


### 4.6 The Aristotelian Argument in a Modern Form




Putting his anti-materialist argument outlined above, in section 1,
in very general terms, Aristotle's worry was that a material organ
could not have the range and flexibility that are required for human
thought. His worries concerned the cramping effect that matter would
have on the range of *objects* that intellect could accommodate.
Parallel modern concerns centre on the restriction that matter would
impose on the range of rational *processes* that we could
exhibit. Some of these concerns are of a technical kind. Godel, for example, believed that his famous theorem showed that there are demonstrably rational forms of mathematical thought of which humans are capable which could not be exhibited by a mechanical
or formal system of a sort that a physical mind would have to be. Penrose (1990) has argued that Turing's halting problem has similar consequences.But there are other less technical and easier to appreciate issues. I will mention four ways in which physicalist theories of thought seem vulnerable to attack by the dualist




(a) At least since the time of Ryle's *Concept of Mind* (1949), it has been assumed that thinking can be handled in a dispositionalist way; so only sensations or 'raw feels' constitute a problem for the physicalist. There has been a rise or revival of a belief in what is now called *cognitive phenomenology*, that is, the belief that thoughts, of whatever kind - beliefs, desires, and the whole range of propositional attitude state - are conscious in a more than behavioural functional sense. This raises problems for physicalism, for, just as it is a problem that direct knowledge of 'what it is like' to experience your sensations is ultimately hidden from anyone else, so *what you are thinking* is directly accessible only privately, once it has been conceded that it has a phenomenology and not just a functional manifestation.




(b) Anything purely physical operates solely according to physical laws operating on its physical properties: it does not, at bottom, operate according to meanings, senses, or propositional content. As a 'thinking machine', it is what Dennett (1987: 61) calls 'a syntactic engine', where 'syntax' is used, somewhat extendedly, to signify merely the physical structure of symbols and the consequent rules of their operation, rather than their meaning. The issue is whether, under this constraint, one can give an account for meaningful communication and understanding at all.




(c) Physicalist theories of thought almost all focus on the model of
computing, and when it comes to making problem solving (as opposed to
simply calculating) computers, computation comes across what is known
as *the Frame Problem*. This is clearly expounded in Dennett
(1984); see also the entry on
 the frame problem. 
The problem is that the 'mechanical mind' can
only follow instructions, cannot see relevance that has not been
strictly encoded.This is often expressed by saying it lacks
'common sense'.




(d) There is what has become known as 'Benacerraf's Problem' (See his
1983). Numbers, it would seem, are abstract objects, yet our
intellects operate with them all the time. How does a physical brain
interact with an abstract entity? A similar problem could be raised
for concepts in general; they are abstract, general entities, not
physical particulars, yet they are the meat and drink of thinking. For
a dualist about intellect there does not appear to be the same
problem. The immaterial intellect is precisely the sort of thing that
can grasp abstract objects, such as numbers and universals - in the
Aristotelian context, the immaterial intellect is the home of
forms. (There is still the issue of how this intellectual capacity of
the immaterial mind relates to sensory consciousness. According to
Aristotle, perception is a wholly embodied process, but for modern
dualists, sensory consciousness is not material. In order to unify the
perceptual and intellectual functions of the mind, traditional
empiricists tended to be imagists, in their theory of thought, in
order to assimilate the intellectual to the sensory, but this
assimilation is rejected by those who believe in a distinct cognitive
phenomenology, as mentioned in (a) above. The issue of how these two
functions of mind are related in dualism is, it seems to me,
insufficiently investigated.) The difficulty in accounting for the
brain's relation to abstract entities explains why most materialists
tend to be nominalists,thus reducing thoughts to concrete particulars
of some kind. (D. M. Armstrong in his (1978) is a striking exception
to this, accepting an *in re* theory of universals.) But if you
do not find either nominalism or Armstrong's causal-functional theory
of thinking convincing, Plato's idea in the *Phaedo* that the
intellect must be such that it can have an affinity with immaterial
things begins to look very plausible.





I will not discuss (a) further, as it is discussed in 
section 5 of the 
entry on 
 phenomenal intentionality, 
An immaterialist response to (d) can be found in Robinson (2011).




Both (b) and (c) seem to draw out the claim that a material system
 lacks understanding. John Searle's famous 'Chinese
 Room' argument (Searle 1980; see also the entry on
 Chinese room argument) 
seems to support this conclusion, at least if the material system
takes the form of a classical computer, manipulating symbols according
to rules. Searle imagines himself in a room with a letter box through
which strings of symbols are posted in, and, following a book of
rules, he puts out symbols which the rules dictate, given the strings
he is receiving. In fact, Searle says, he has been conducting a
conversation in Chinese, because the symbols are Chinese script, and
the rules those on which a Chinese computer might work, but he has not
understood a word. Therefore neither does a computer understand, so
we, understanding creatures, are not computers. If Searle is right,
this is the end for the classical 'syntactic engine' as a
model for thought.




A blow was struck against the computational theory of thought when, in
2000, Fodor produced his *The Mind Does Not Work That Way*, in
which he made clear his belief that the kind of computationalism that
he had been describing and developing ever since the 1970s only fits
sub-personal informational processing, not conscious, problem solving
thought. I say that he 'made this clear', because he had
always mentioned this reservation, but his claim that what he was
describing was 'the Language of Thought' led his readers
generally to take him to be proposing an account of what we normally
consider to be thinking, which is not restricted (even if it includes
at all) sub-personal processes. The modest view it is entirely in line
with his close colleague Chomsky's claim that his
- Chomsky's - linguistic theories cannot touch the 'creative
use of language'(See Baker, 2011).




One physicalist response to these challenges is to say that they apply
only to the classical computing model, and are avoided by
connectionist theories. Classical computing works on rules of
inference like those of standard logic, but connectionism is rather a
form of associationism, which is supposedly closer to the way in which
the brain works.(See the entry on Connectionism.) The latest version
of this - 'Deep Learning' - is very good at
face recognition and, in general, pattern recognition, including those
involved in the playing of games like chess and Go. But Gary Marcus
(2018 - see Other Internet Resources) and others have pointed
out the ways in which these impressive machines are quite different
from human thought. Marcus points to ten significant differences, but
the two most easy to capture briefly are (i) 'deep
learning' is data hungry. We can learn things with very few
trials because we latch on to abstract relationships, whereas the
machine requires many - perhaps thousands or millions - of
examples to try to catch extensionally what we get by the abstract or
intensional relation. (ii) Deep learning is shallow and has a limited
capacity for transfer of what it has learnt from one context to
another, even though the differences look trivial to us. It seems
that collecting examples cannot itself constitute 'getting the
point', though it might manage to mimic it, if the circumstances
are carefully managed.




The dualist might sum up the situation on thought in the following way. The case against physicalist theories of sensation is that it is unbelievable that *what it feels like* to be struck hard on the nose is itself either just a case of being disposed or caused to engage in certain behaviours, or that *what it feels like* is not fundamental to the way you do react. Similarly, the dualist about thought will say, when you are, for example, engaged in a philosophical discussion, and you make a response to your interlocutor, it is obvious that you are intending to respond to *what you thought he or she meant* and are concentrating on what *what you intend to say* means. It seems as bizarre to say that this is a bye-product of processes to which meaning is irrelevant, as it is to claim the same about sensory consciousness. You are, in other words, as fundamentally a semantically driven engine, as you are a sensorily consciously driven one. Perhaps, in the case of a sophisticated conversation, the fundamentality of meaning, and of conscious reflection, as a driver is even more obvious than in the case of sensation




A dualist could, it seems, argue that Plato was right in claiming that intellect necessarily has an affinity with the realm of abstract entities, and Aristotle was right to think that no material or mechanical system could capture the flexibility built into genuine understanding. We all have our limitations, but there is no specific point, following directly from what we are made of, or how we are 'programmed' which constitutes an absolute barrier.


## 5. Problems for Dualism




We have already discussed the problem of interaction. In this
section we shall consider two other facets of dualism that worry
critics. First, there is what one might term the *queerness* of
the mental if conceived of as non-physical. Second there is the
difficulty of giving an account of the unity of the mind. We shall
consider this latter as it faces both the bundle theorist and the
substance dualist.


### 5.1 The Queerness of the Mental




Mental states are characterised by two main properties,
subjectivity, otherwise known as privileged access, and intentionality.
Physical objects and their properties are sometimes observable and
sometimes not, but any physical object is equally accessible, in
principle, to anyone. From the right location, we could all see the
tree in the quad, and, though none of us can observe an electron
directly, everyone is equally capable of detecting it in the same ways
using instruments. But the possessor of mental states has a privileged
access to them that no-one else can share. That is why there is a
sceptical 'problem of other minds', but no corresponding
'problem of my own mind'. This suggests to some
philosophers that minds are not ordinary occupants of physical
space.




Physical objects are spatio-temporal, and bear spatio-temporal and
causal relations to each other. Mental states seem to have causal
powers, but they also possess the mysterious property of 
intentionality - being *about* other things - including things 
like Zeus and the square root of minus one, which do not exist. No mere
physical thing could be said to be, in a literal sense,
'about' something else. The nature of the mental is both
queer and elusive. In Ryle's deliberately abusive phrase, the mind, as
the dualist conceives of it, is a 'ghost in a machine'.
Ghosts are mysterious and unintelligible: machines are composed of
identifiable parts and work on intelligible principles. But this
contrast holds only if we stick to a Newtonian and common-sense view of
the material. Think instead of energy and force-fields in a space-time
that possesses none of the properties that our senses seem to reveal:
on this conception, we seem to be able to attribute to matter nothing
beyond an abstruse mathematical structure. Whilst the material world,
because of its mathematicalisation, forms a tighter abstract system
than mind, the sensible properties that figure as the objects of mental
states constitute the only intelligible content for any concrete
picture of the world that we can devise. Perhaps the world within the
experiencing mind is, once one considers it properly, no 
more - or even less - queer than the world outside it.


### 5.2 The Unity of the Mind




Whether one believes that the mind is a substance or just a bundle
of properties, the same challenge arises, which is to explain the
nature of the unity of the immaterial mind. For the Cartesian, that
means explaining how he understands the notion of immaterial substance.
For the Humean, the issue is to explain the nature of the relationship
between the different elements in the bundle that binds them into one
thing. Neither tradition has been notably successful in this latter
task: indeed, Hume, in the appendix to the *Treatise*, declared
himself wholly mystified by the problem, rejecting his own initial
solution (though quite why is not clear from the text).


#### 5.2.1 Unity and Bundle Dualism




If the mind is only a bundle of properties, without a mental
substance to unite them, then an account is needed of what constitutes
its unity. The only route appears to be to postulate a primitive
relation of co-consciousness in which the various elements stand to
each other.




There are two strategies which can be used to attack the bundle
theory. One is to claim that our intuitions favour belief in a subject
and that the arguments presented in favour of the bundle alternative
are unsuccessful, so the intuition stands. The other is to try to
refute the theory itself. Foster (1991, 212-9) takes the former path.
This is not effective against someone who thinks that metaphysical
economy gives a prima facie priority to bundle theories, on account of
their avoiding mysterious substances.




The core objection to bundle theories (see, for example, Armstrong
(1968), 21-3) is that, because it takes individual mental contents as
its elements, such contents should be able to exist alone, as could the
individual bricks from a house. Hume accepted this consequence, but
most philosophers regard it as absurd. There could not be a mind that
consisted of a lone pain or red after-image, especially not of one that
had detached itself from the mind to which it had previously belonged.
Therefore it makes more sense to think of mental contents as *modes
of a subject*.




Bundle theorists tend to take phenomenal contents as the primary
elements in their bundle. Thus the problem is how to relate, say, the
visual field to the auditory field, producing a 'unity of
apperception', that is, a total experience that seems to be
presented to a single subject. Seeing the problem in this way has
obvious Humean roots. This atomistic conception of the problem becomes
less natural if one tries to accommodate other kinds of mental activity
and contents. How are acts of conceptualising, attending to or willing
with respect to, such perceptual contents to be conceived? These kinds
of mental acts seem to be less naturally treated as atomic elements in
a bundle, bound by a passive unity of apperception. William James
(1890, vol. 1, 336-41) attempts to answer these problems. He claims to
introspect in himself a 'pulse of thought' for each present
moment, which he calls 'the Thought' and which is the
'vehicle of the judgement of identity' and the
'vehicle of choice as well as of cognition'. These
'pulses' are united over time because each
'appropriates' the past Thoughts and 'makes us say
"as sure *as I exist*, those past facts were part of myself".
James attributes to these Thoughts acts of judging, attending, willing
etc, and this may seem incoherent in the absence of a genuine subject.
But there is also a tendency to treat many if not all aspects of agency
as mere awareness of bodily actions or tendencies, which moves one back
towards a more normal Humean position. Whether James' position really
improves on Hume's, or merely mystifies it, is still a moot point. (But
see Sprigge (1993), 84-97, for an excellent, sympathetic
discussion.)


#### 5.2.2 Unity and Substance Dualism




The problem is to explain what kind of a thing an immaterial
substance is, such that its presence explains the unity of the mind.
The answers given can be divided into three kinds.




(a) The 'ectoplasm' account: The view that immaterial
substance is a kind of immaterial stuff. There are two problems with
this approach. First, in so far as this 'ectoplasm' has any
characterisation as a 'stuff' - that is, a structure
of its own over and above the explicitly mental properties that it
sustains - it leaves it as much a mystery why *this* kind
of stuff should support consciousness as it is why ordinary matter
should. Second, and connectedly, it is not clear in what sense such
stuff is immaterial, except in the sense that it cannot be integrated
into the normal scientific account of the physical world. Why is it not
just an aberrant kind of physical stuff?




(b) The 'consciousness' account: The view that consciousness is the
substance. Account (a) allowed the immaterial substance to have a
nature over and above the kinds of state we would regard as mental. The
consciousness account does not. This is Descartes' view. The most
obvious objection to this theory is that it does not allow the subject
to exist when unconscious. This forces one to take one of four possible
theories. One could claim (i) that we are conscious when we do not seem
to be (which was Descartes' view): or (ii) that we exist
intermittently, though are still the same thing (which is Swinburne's
theory, (1997), 179): or (iii) that each of us consists of a series of
substances, changed at any break in consciousness, which pushes one
towards a constructivist account of identity through time and so
towards the spirit of the bundle theory: or (iv) even more
speculatively, that the self stands in such a relation to the normal
time series that its own continued existence is not brought into
question by its failure to be present in time at those moments when it
is not conscious within that series (Robinson, forthcoming).




(c) The 'no-analysis' account: The view that it is a mistake to
present any analysis. This is Foster's view, though I think Vendler
(1984) and Madell (1981) have similar positions. Foster argues that
even the 'consciousness' account is an attempt to explain
what the immaterial self is 'made of' which assimilates it
too far towards a kind of physical substance. In other words, Descartes
has only half escaped from the 'ectoplasmic' model. (He
*has* half escaped because he does not attribute non-mental
properties to the self, but he is still captured by trying to explain
what it is made of.)




Foster (1991) expresses it as follows:



> ...it seems to me that when I focus on myself
> introspectively, I am not only aware of being in a certain mental
> condition; I am also aware, with the same kind of immediacy, of being a
> certain sort of thing... 
> 
> 
> 
> It will now be asked: 'Well, what *is* this nature,
> this sortal attribute? Let's have it specified!' But such a
> demand is misconceived. Of course, I can give it a verbal label: for
> instance, I can call it 'subjectness' or
> 'selfhood'. But unless they are interpreted
> 'ostensively', by reference to what is revealed by
> introspective awareness, such labels will not convey anything over and
> above the nominal essence of the term 'basic subject'. In
> this respect, however, there is no difference between this attribute,
> which constitutes the subject's essential nature, and the specific
> psychological attributes of his conscious life...
> 
> 
> 
> 
> Admittedly, the feeling that there must be more to be said from a
> God's eye view dies hard. The reason is that, even when we have
> acknowledged that basic subjects are wholly non-physical, we still tend
> to approach the issue of their essential natures in the shadow of the
> physical paradigm. (243-5)
> 
> 
> 




Berkeley's concept of *notion* again helps here. One can
interpret Berkeley as implying that there is more to the self than
introspection can capture, or we can interpret him as saying that
notions, though presenting *stranger* entities than ideas,
capture them just as totally. The latter is the 'no account is
needed' view.