A Priori Physicalism, Lonely Ghosts and Cartesian Doubt

Two kinds of imaginary friend philosophers play withMany of my friends like to play with zombies. Zombies are physical duplicates of actual human

beings with no conscious experience.

Instructions for conceiving of zombies: Bring to mind an exact physical

duplicate of an actual human being, but suppose that there's nothing that it's

like to be the thing you're conceiving of.

I find it difficult to conceive of zombies. The first problem is I don't know enough neuroscience.

The second problem is no one knows enough neuroscience. Let us say that one can 'fully conceive'

of X if and only if it's not the case that one's conception of X can be made more complete with more

empirical information. None of us has a complete understanding of the physical workings of the

body and brain, and in the absence of such an understanding one cannot fully conceive of zombie; if

one cannot fully conceive of a physical duplicate of an actual human, then one cannot fully

conceive of a physical duplicate of a an actual human with no consciousness.

The fact that we can't fully conceive of zombies makes any argument which starts from the

conceivability of zombies susceptible to what I call 'the Wait and See Response':

The Wait and See Response: Until we know all the physical facts, we

cannot know whether zombies will turn out to be fully conceivable.

Perhaps now it seems intuitive that zombies are fully conceivable, but our knowledge of the brain is

radically incomplete. Maybe on the mythical day in the far flung future when neuroscience is

complete we'll discover that zombies are not in fact fully conceivable. The power of this objection

lies in its pointing to the fact that zombie arguments are grounded in intuitions about an epistemic

state we can't yet get into: i.e. the state of fully conceiving of all the physical facts about some

actual individual (the intuition being that someone in this state could coherently suppose that the

thing they are conceiving of lacked consciousness).

I prefer to play with lonely ghosts. A lonely ghost is a being that has the following four

characteristics: (i) it is the only contingent thing that exists, (ii) it only exists for a short time, (iii) it

has conscious states, (iv) it has no (fundamental, non-trivial) properties other than its determinate

state of consciousness. When I tell my friends that I like to imagine lonely ghosts, they initially

express astonishment, and profess that they could not begin to be able to engage in such

entertainment themselves. But it's easy when you know how.

Instructions for conceiving of lonely ghosts: Engage in

Cartesian doubt. Consider all the propositions you believe. For

each proposition such that you can't be completely certain that

it's true, suppose that it's false, and continue to suppose that it's

false for the rest of the exercise. Continue with the exercise up to

and including the time you find yourself entertaining

propositions with the knowledge that they are certainly true.

When I set aside a little time to honestly and earnestly engage in Cartesian doubt, it has the

following result. I find I can doubt that I am in a drab flat typing away on a laptop. I can doubt that I

have hands, or a body or even a brain. But I cannot doubt that I have a conscious experience as of

being in a drab flat typing away on a laptop. I cannot doubt that I have a conscious experience as of

having hands and a body. I can doubt that there are any aspects of my nature over and above my

conscious states, but I cannot doubt that I exist as a conscious thing: as a thing such that there's

something that it's like to be it. I can doubt that this conscious thing existed in the recent past

(perhaps it just popped into existence) or that it will continue to exist in the near future (perhaps it

will soon pop out of existence); in fact I can doubt that there is any contingent being at all outside of

myself existing as a conscious thing. But I cannot doubt that I exists in the present moment as a

conscious thing.

When I reflect on the epistemic state I have got myself into when I get to the end of this rather

peculiar process, I find that it is one in which I am conceiving of myself as a lonely ghost. Because

I can doubt the existence of anything in my past or my future, or anything outside of myself in the

present moment, it follows that I am conceiving of myself as having characteristics (i) and (ii) of a

lonely ghost. Because I am cannot doubt that I have conscious states, but I can doubt that there are

any aspects of my nature over and above my conscious states, it follows that I am conceiving of

myself as something that has characteristics (iii) and (iv) of a lonely ghost. At the end of the process

of Cartesian doubt I find I am conceiving of myself as a lonely ghost; ergo I am conceiving of a

lonely ghost.

And note that I am fully conceiving of a lonely ghost at the end of this process. There is no

empirical information I could learn which would make my conception more complete. This is not to

say that further reflection will not improve my conception, or perhaps reveal within it some

incoherence. It is difficult ever to be completely certain that what one is conceiving of is ideally

conceivable, that is, would remain conceivable upon maximal reflection. However, if something is

fully conceivable, and our best efforts of reflection do not reveal any incoherence, I think this is

very good grounds for concluding that what we are conceiving of is ideally conceivable. I can fully

conceive of a million sided object, and careful and sustained thought does not reveal any

incoherence in the notion. I thus feel I have good justification for taking a million sided object to be

ideally conceivable. I feel exactly the same about the state of affairs I end up conceiving of at the

end of the process of Cartesian doubt.

Why ghosts are scarier than zombiesGhostly arguments, that is arguments which start from the conceivability of lonely ghosts, are

superior to zombie arguments, that is arguments which start from the conceivability of zombies, in

the following two respects.

Firstly, lonely ghosts are fully conceivable, whereas zombie, at least at this stage of our knowledge,

are not. Because of this zombie argument are, but ghostly arguments are not, susceptible to the Wait

and See Response. Zombie arguments are grounded in an intuition about an epistemic state we can't

as yet get ourselves into, the state of fully conceiving of all the physical facts about a given

individual. Ghostly arguments are grounded in an epistemic state we arguably can get into here and

now, the state of fully conceiving of lonely ghosts.

Secondly, if someone claims they can't conceive of a zombies, there is very little that can be said to

try to persuade them. If someone claims they can't conceive of a lonely ghost, there is a way to try

to persuade them:

'What happens when you engage in Cartesian doubt? Don't you find that you

can doubt the existence of everything outside of anything in the future and

the past, and anything outside of yourself in the present moment? Don't you

find that you can't doubt that you exist as a thing with conscious states, but

you can doubt that there are any aspects of your nature over and above your

conscious states? Aren't you then conceiving of yourself as a lonely ghost?'

My opponent is obliged to answer these questions. If they still think they can't conceive of a lonely

ghost, then they ought to tell me some alternative story about what happens when they engage in

Cartesian doubt. They have to tell me whether they stop earlier or later than I do. If they agree with

me about where Cartesian doubt stops, then need to tell me why, when they reach that point, they

think they are not conceiving of themselves as a lonely ghost. My story about Cartesian doubt is

quite intuitive; my opponent has to try to make some alternative intuitive. Of course, we may end up

at some other clash of intuitions; still there is this extra dimension of dialectical force not present in

the zombie case.

I would consider a fellow philosopher disingenuous if she claimed to be completely unable

understand why people are attracted to my view of Cartesian doubt, call it the Cartesian view of

Cartesian doubt. The Cartesian view of Cartesian doubt is of course not uncontentious, but I do

think it ought to be seen as the default position. Most people, and I include here reflective children,

when they try to engage in Cartesian doubt, find themselves drawn to something like the Cartesian

view: roughly, one can doubt the body and the material world, but one cannot doubt the mind. The

first two of Descartes' Meditations, whatever faults they might ultimately have, are very intuitive.1

Few people read Meditations 1 and 2 and find themselves thinking, 'I don't know where he's going

with this...I can't get into Descartes' mindset at all!'. Rather it's very easy to let yourself follow

Descartes intuitions.

Of course many philosophers, those in the tradition following Wittgenstein for example, will want

to say that there are certain confusions we naturally incline towards when we start thinking

philosophically, and the tendency towards the Cartesian view of Cartesian doubt is to be explained

in terms of these confusions. I certainly do not want to dismiss this kind of view out of hand. But I

do think the onus is on such a philosopher to demonstrate this, to tell me where the confusion lies.

In the absence of such a demonstration, the Cartesian view of Cartesian doubt should be seen as the

intuitive default position.

Why a priori physicalists should fear ghostsA priori physicalism is the view that all facts are a priori entailed by the physical facts. If you had

the complete physical description of the world, and you were clever enough, and you had all the

relevant concepts, then you would be able to work out all the other truths about the world: chemical

biological, sociological, economic. You could work out that water is H2O, that there was world

economic crisis in 2008, that Cliff Richard's real name is Harry Webb, etc. 1 Descartes, R. (1996) Meditations on First Philosophy, edited by J. Cottingham, Cambridge: Cambridge University

Press.

It is generally agreed on all sides that consciousness is a particularly troubling phenomenon for the

a priori physicalist. Many have a strong intuition that you could know all the physical facts about

Jake, you could cut open his head and learn everything there was to know about the

neurophysiological workings of his brain, and you still wouldn't know with 100% certainty whether

or not Jake was conscious. I take it that this is why we have a sceptical problem of other minds, as

distinct from any other sceptical concerns about the world around us. But of course if we can know

all the relevant physical facts about Jake, and yet not know with 100% certainty whether or not Jake

was conscious, then the physical facts do not entail the facts about Jake's conscious life.

So it is generally agreed that the a priori physicalist ought to give some account of our mental

concepts from which it follows that the physical facts entail the facts about consciousness. The a

priori physicalist has to, as it were, map out the conceptual meeting point of the physical and the

phenomenal. If the a priori physicalist has nothing to say in this regard, her view remains pretty

implausible. I think that every such conceptual meeting point ever proposed by an a priori

physicalist is incompatible with the conceivability of ghosts. In this paper, I will try to demonstrate

the incompatibility of lonely ghosts with two well known forms of a priori physicalism: analytic

functionalism and Australian physicalism.2

Analytic functionalismAnalytic functionalism is probably the simplest form of a priori physicalism, the crudest way of

mapping out the conceptual meeting point of the physical and the mental. I understand it to be the

view that the concept of a mental state and conscious states are a subset of mental states is the

concept of a higher-level functional state; to suppose that someone has a certain conscious state is

just to suppose that they have some inner state that plays a certain causal role. For example, to

suppose that someone is in pain is to suppose that they have some inner state which 'plays the pain

role', i.e. mediates between bodily damage and avoidance behaviour in the distinctive way pain

does.3

I hope it is clear why analytic functionalism counts as a form of a priori physicalism. Assuming its

truth, we could open up Jake's head, study his brain, find out the causal profiles of his brain states,

2 This paper is adapted from a chapter of a monograph I am working on, the first half of which argues against physicalism. In that chapter I also try to show how the conceivability of ghosts is inconsistent with Fred Dretske's naturalistic representationalism.

3 See Putnam, H. (1973) 'Psychological predicates,' in Capitan, W. H. & Merrill, D. D. (Eds.) Art, Mind, and Religion, University of Pittsburgh Press, 38-48, reprinted in Chalmers, D. (2002) (Ed.) Philosophy of Mind: Classical and Contemporary Readings, Oxford, New York, Oxford University Press, 73-87.

discover that one of them plays the pain role, and thereby deduce that Jake is in pain. Assuming the

truth of analytic functionalism, the physical facts entail the facts about consciousness.

My argument that analytic functionalism is incompatible with the conceivability of lonely ghosts

starts from the following premise: lonely ghosts don't have causal capacities. Let me try to justify

this claim. It is philosophically controversial what a causal capacity is, and even what our concept

of a causal capacity is. But I think that, when we reflect on all the going philosophical theories of

causation and causal concepts, we discover that there is nothing recognisable as a causal capacity in

the world of a lonely ghost.

We can divide theories of causation into two broad camps: Humean and non-Humean. Humean

theories ground laws and causation in regularities throughout space and time; such views range

from the crude regularity view, to the more sophisticated counterfactual theory of causation.4 Non-

Humean theories ground causation in natural necessity. In the non-Humean camp there are those

who believe in brute causal capacities, perhaps the brute capacity of salt to dissolve in water, or

electrons to repel each other,5 and those who adopt the Armstrong-Tooley-Dretske view of laws,

according to which laws of nature are constituted of contingent relations of natural necessitation

holding between universals.6

Return again to the four characteristics of a lonely ghost. I think (i) and (ii) rule out a lonely ghosts

having causal capacities on any Humean conception of causal capacities; a lonely ghost is alone in

its universe; there just aren't the kind of regularities in its world needed to ground laws and

causation on any Humean conception of these things. I think (iii) and (iv) rule out a lonely ghost's

having causal capacities on any non-Humean conception of such things. A ghost's nature is

exhausted by conscious experience. It follows that it has no brute causal capacities, as these would

be aspects of its nature over and above its conscious states. Perhaps one might argue that a ghost

instantiates universals, on the grounds that realism about universals is the only coherent theory of

properties. But certainly a ghost's universals do not stand in relations of contingent necessitation, as

again this would constitute an extra aspect of a ghost's nature over and above conscious experience.

I conclude, therefore, that a lonely ghost has no causal capacities: when one reaches the end of

4 Lewis, D. 1973. 'Causation', Journal of Philosophy 70: 17, 556-67.5 For example, Ellis, B. (2001) Scientific Essentialism, Cambridge: Cambridge University Press; Ellis, B. (2002) The

Philosophy of Nature, Chesham: Acumen.6 Armstrong, D. M. (1983) What is a Law of Nature? Cambridge: Cambridge University Press.; Dretske, F (1977)

Laws of Nature, Philosophy of Science 44; Tooley, M. (1977) The Nature of Laws, Canadian Journal of Philosophy.

Cartesian doubt, one ends up conceiving of oneself as a thing which has no causal powers. It

follows that one can conceive of something which has conscious states, but no causal powers. But if

one can conceive of something which has conscious states but no causal powers, then our mental

concepts (or at least those which denote conscious states) cannot be functional concepts. If to

conceive of something in pain were just to conceive of something which has some inner state that

plays the pain role, then it would not be possible to conceive of something which is in pain but has

no causal capacities; that would be contradictory: it would be to conceive of something which has a

state that plays the pain role but doesn't have a state which plays the pain role (as it doesn't have any

causal capacities). The conceivability of lonely ghosts is incompatible with the truth of analytic

functionalism.

Australian physicalismAustralian physicalism resembles analytic functionalism in holding that our mental concepts are a

priori associated with causal role concepts, and that they refer in virtue of this association.

However, whilst analytic functionalist think that mental states are higher-level functional states,

Australian physicalists hold that mental states are the actual realisers of high-level functional

states.7

Suppose Jake is in pain. Both analytic functionalist and Australian physicalist will agree that there

are two properties in play here (at least on some metaphysically loose understanding of 'property'):

there is some physical property which plays the pain role, let's suppose that that property is c-fibre

firing, and there is the functional property, call it 'F', of having some property which plays the pain

role. The two views just disagree on which of these two properties is to be labelled 'pain'. The

analytic functionalist says that F is pain, whilst the Australian physicalist says that c-fibre firing is

pain.

One key feature of the Australian physicalist position is that according to it pain might not have

been pain, as the term 'pain' is a flaccid designator: it refers to different states in different possible

worlds (in the same way, all mental states might not have been mental states, as mental terms are

flaccid designators). Compare to something which is more obviously an example of a flaccid

designator, the term 'US president in 2010'. In the actual world this term picks out Barak Obama.

However, there is another world, call it W, where McCain won the last election, and in that world

'US president in 2010' picks out McCain rather than Obama. The term 'US president in 2010' picks

out, in each world, whoever won the most recent election in 2010 in that world.7 See, Armstrong, D. M. 1968. A Materialist Theory of Mind, Routledge, and Lewis, D. 1994. 'Reduction of Mind', in

S. Guttenplan, Companion to the Philosophy of Mind, Blackwell, 412-31.

Similarly, according to Australian physicalists, 'pain' picks out, in each world, whatever state plays

the pain role in that world. Perhaps in the actual world 'pain' picks out c-fibre firing, as that state

actually plays the pain role. However, perhaps in W the laws of nature are different, and pain plays

the pleasure role rather than the pain role. In this case, in W 'pain' does not pick out c-fibre firing,

but perhaps picks out some other physical state (that other physical state, if there is one, that plays

the pain role).

Can Australian physicalists make sense of the conceivability of ghosts? Remember that the problem

for the analytic functionalist was that their view entailed that one cannot conceive of thing with no

causal capacities instantiating mental states. The Australian physicalist might claim to be on better

ground here, as there is at least a sense in which this can be done on her view:

We conceive of pain as the thing that actually plays the pain

role, but this is consistent with conceiving of it in worlds where

it doesn't play the pain role. Compare: we may conceive of

Obama as the actual 2010 US president, but this is consistent

with conceiving of him in worlds where he didn't win the last

election. When you are conceiving of a lonely ghost in pain,

you are just conceiving of the state which actually plays the

pain role in a world where it doesn't play the pain role. The

same goes for all the other mental states a ghost instantiates;

when you are conceiving of a lonely ghost you are conceiving

of a thing with actual mental states in a world where they lack

the causal profiles which characterise them in the actual world.

No worries! That's perfectly consistent with our view.

I have two concerns with this reply.

My first worry is as follows. Perhaps there is a sense in which the Australian physicalist can make

sense of pain existing in a world where there is no causation. But in that world it isn't pain! It

doesn't hurt! If that sounds paradoxical, return again to our comparison. We can conceive of the

actual president, i.e. Obama, in worlds where he didn't win the election, but in those worlds he isn't

president. In any world, anything that didn't win the election in that world isn't president in that

world. Similarly, in any world, anything that doesn't play the pain role in that world isn't pain in that

world (assuming the truth of Australian physicalism).

But suppose I am in agony, and I engage in Cartesian doubt. I find I cannot doubt that I am in

agony, but I can doubt that I have causal capacities. I don't end up conceiving of a thing which has

actual pain that doesn't hurt. Rather I end up conceiving of a world where there is a thing with a

state that in the world I am conceiving of really hurts. The same goes for all other mental states.

When I reach the end of Cartesian doubt, I am conceiving of a world in which there is a thing that

has states that in that world I am conceiving of are mental states.

Let me then make the definition of a lonely ghost slightly more precise by making characteristic

(iii) of a lonely ghost slightly more precise: a lonely ghost has states such that, in the world in

which it exists, are conscious states. Given this more precise definition of a lonely ghost, Australian

physicalists cannot make sense of their conceivability. They can perhaps make sense of the

conceivability of a world where there is a thing which does not have causal capacities but

nonetheless has mental states (or rather states that are mental states in the actual world), but they

cannot make sense of the conceivability of a world where there is a thing which has no causal

capacities but which nonetheless has states which in the world being conceived of are mental states.

Australian physicalism, then, is inconsistent with the conceivability of lonely ghosts (according to

this more precise definition).

My second worry relies on the distinction in two-dimensional semantics between conceiving of a

world as actual and conceiving of a world as counterfactual.8 Australian physicalists can only make

sense of the conceivability of mentality in the absence of causality in worlds conceived of as

counterfactual; when I am conceiving of pain that doesn't play the pain role I am conceiving of the

actual thing that plays the pain role in some counterfactual world where it doesn't play the pain role

(on their view). It would of course not be possible to conceive of the thing that actually plays that

pain role not actually playing the pain role, in the same way it isn't possible to conceive of the thing

that actually won the most recent US election not actually winning that election.

But when I reach the end of Cartesian doubt, I am conceiving of a way the actual world might

conceivably turn out to be. I can doubt that I have causal capacities, but I can't doubt that I have

conscious states. Therefore, it is conceivable that the actual world turn out to be one in which I have

conscious states but do not have causal capacities.

8 Chalmers, D. J. 1996. The Conscious Mind: Towards a Fundamental Theory, Oxford: Oxford University Press; Jackson, F. 1998. From Metaphysics to Ethics: A Defence of Conceptual Analysis, Clarendon Press: Oxford.

Even if Australian physicalists can make sense of the conceivability of lonely ghosts (which my

first worry casts doubt on), they cannot make sense of the conceivability of lonely ghost as actual.

The conceivability lonely ghosts as actual is inconsistent with Australian physicalism.