Dualism: from an explanatory to an ontological gap

Property dualism: at least some mental properties are fundamental, i.e. not identical to any non-mental properties, like neurochemical or functional properties. Typically, property dualists contend, against materialists, that what philosophers call a phenomenal state, i.e. the undergoing of an experience with a distinctive qualitative character, is not identical to any neurochemical (or functional) state. For example, an experience of pain is not identical to the undergoing of C-fibre stimulation, even if C-fibre stimulation always occurs when we experience pain, and vice versa. Hence, the phenomenal property of being in a state of pain is not identical to the neurochemical property of being in a state of C-fibre stimulation, or any other neurochemical (or functional) property. As we have seen, property dualists generally argue that there is an unbridgeable explanatory gap between neurochemical and phenomenal facts. That is, we lack an explanation as to how it is that phenomenal states 'just are' neurochemical states. If two things X and Y are numerically identical, then it is logically impossible for one to exist without the other. Thus, we may say that a logically necessary connection holds between X and Y, such that the existence of X logically entails that of Y, and vice versa. The dualist complaint is that there is no explanation as to why such a connection should hold between, say, the state of experiencing pain and the state of undergoing C-fibre stimulation. For many dualists, this is strong reason to reject the thesis that the state of experiencing pain 'just is' the state of undergoing C-fibre stimulation, as well as all identifications of phenomenal states with neurological ones.

We can reconstruct the argument as follows:

(1) There is no explanation as to how phenomenal states are identical to neurochemical states.

(2) If there is no explanation as to how phenomenal states are identical to neurochemical states, phenomenal states are not identical to neurochemical states. (3) Therefore, phenomenal states are not identical to neurochemical states. Notice that the argument's begins with the statement of an explanatory gap (premise (1) ) and ends with the statement of an ontological gap (conclusion (3) ). That is, the argument, through premise (2), infers a claim about the manner in which things exist, from a claim about a lack of explanation. As some materialist critics of the argument have shown, e.g. Papineau 1998, one can try to block this inference by putting pressure on premise (2). One can accept the argument's first premise, but deny that the ontological gap follows from the explanatory gap, by arguing that the demand for an explanation is unreasonable. If two things X and Y are identical, it makes sense to ask how we know that they are identical, but it seems odd to ask why they are identical. For example, if you tell me that Bruce Wayne is Batman, I may ask you how you know this, but you'd be surprised if I asked you, 'But why is Bruce Wayne Batman?' You might interpret my question along the lines of 'Why did Bruce Wayne become a masked vigilante?', but you'd be very puzzled if I replied with 'No, I mean why is the person Bruce Wayne the same person as the person Batman?'. This is like asking, 'why am I the same person as myself?'. Things just are what they are, and, on the face of it, it makes little sense to ask why this is so. Thus, it could be argued, the absence of an explanation for the identity of, say, the experience of pain and C-fibre stimulation is nothing to be worried about, and, against premise (2), certainly shouldn't lead us to deny that they are identical. I think this objection rests on an ambiguity in the request for an 'explanation'. If I ask you to explain to me why my phone has disappeared, I am asking you to give me the cause of my phone's disappearance, i.e. the prior event or fact that brought about its disappearance. If on the other hand I ask you to explain Spinoza's theory that God is the only substance, I am asking you to make the theory intelligible to me.

The way I see it, the 'explanatory gap' problem is not that we know of no prior cause of the identity between the experience of pain and C-fibre stimulation, but rather that such an identification is unintelligible. If things X and Y are identical, their identity, while not 'caused', is nevertheless made true by some other fact. The identity of Batman and Bruce Wayne is made true by the fact that they are the product of the same particular fertilization event, i.e. involving the same sperm and egg. The fact that my Dad's car today is the same as the car that existed three years ago is made true by the fact that there is some special kind of causal continuity between the two. Given such facts, the non-identity of X and Y is inconceivable: for example, given that Batman and Bruce Wayne are the product of the same particular fertilisation event, it is impossible to conceive of their non-identity. Arguably, it is part of the very concept of identity that identity-claims be made true by some other fact in this way. And therein lies the problem for the identification of the experience of pain with C-fibre stimulation: materialists cannot give us any fact by which the relevant identity-claim is made true. This is why thought experiments about, say, the conceivability of C-fibre stimulation existing without the experience of pain, or vice versa, are so prominent in the case for dualism. If the experience of pain and C-fibre stimulation were identical, there would be some fact given which it would be impossible to conceive of one without the other. But, we know of no such fact, and we can't even conceive of a fact that would do the job. This last point allows us to deal with a common rejoinder to dualist arguments. It used to be thought that the Morning Star and the Evening Star were two different stars, though we now know that they are in fact the same planet, Venus. But before this discovery, people presumably would have been able to conceive of the Morning Star existing without the Evening Star, or vice versa (or, at any rate, it would have seemed to them that they could conceive of this). Hence, we are told, the conceivability of pain without C-fibre stimulation, or vice versa (or the appearance of this conceivability), is no good reason to disbelieve that they are the same thing. But there is a key difference between the two cases: if I was born before the discovery of the identity of the Morning Star with the Evening Star, I wouldn't know how they are identical, but, after a bit of thinking, I would know how they could be identical. That is, I could imagine that they are the result of the same particular planet-formation event, and understand that this would entail that they are the same thing, though perceived from different perspectives. Indeed, I would understand that, if it were the case that they were the result of the same particular planet-formation event, the existence of one without the other would be inconceivable. In contrast, in the case of pain and C-fibre stimulation, I can't even see what sort of fact would make true the statement of their identity, and hence do not understand how they could be identical. I can think of no possible neurochemical (or other) state of affairs such that, if it obtained, the existence of C-fibre stimulation without the experience of pain would be inconceivable. It is in this sense, I think, that the (alleged) identity of phenomenal states and neurochemical states lacks an explanation: it is unintelligible, because we cannot see how they could be identical. And if that's right, then it seems to me that, insofar as a metaphysical system ought to minimize unintelligible claims, this is strong reason to reject the identification of phenomenal states with neurochemical states. This, in my view, is how the explanatory gap leads us to an ontological gap.

How property dualism leads to substance dualism

Call property dualism the theory that at least some mental properties are fundamental. That is, at least some mental properties are not identical to neurochemical or functional properties (or any other, non-mental properties). For example, property dualism is true if the mental property of being in pain, cannot be identified with a neurochemical property like being in C-fibre stimulation, or a functional property like being in the state of 'screaming and quickly removing one's hand from the hot stove' (or any other property other than 'being in pain'). Thus, property dualists say that some mental properties -- usually conscious, or phenomenal properties -- are irreducible. 'Being in pain' is just that -- 'being in pain', and nothing else. Call substance dualism the theory that selves are fundamental. That is, I, i.e. my 'self', am not identical to my (living) body, or my brain, or anything other than I. Hence, it is at least in principle possible for me to exist without my (living) body, and even without my brain. Thus, substance dualists say that a self is irreducible. I am just 'I', and nothing else. Traditionally, the self is thought to bear mental properties, in the way that ordinary objects are thought to bear properties like solidity or colour. To use a common metaphor, the self is supposed to be the seat of mental properties. Substance dualism is arguably the 'default', intuitive view of the self. Humans of all cultures and backgrounds have always imagined ghosts and other disembodied spirits, but such things would be impossible in principle if a self is just a living body. Interestingly enough, the implicit assumption of substance dualism in the hugely popular science-fiction TV series Black Mirror shows that the theory's intuitive appeal is alive and well (cf. season 3, episode 4 San Junipero). Philosophers, on the other hand, aren't quite as enthusiastic about substance dualism. It is true that property dualism has experienced a striking resurgence in recent times, thanks to the work of dualist philosophers like David Chalmers and Thomas Nagel. Such 'neo-dualists' have persuasively argued that phenomenal properties, like the property of being in pain are irreducible. But the majority of philosophers still reject dualism of any kind. And even the neo-dualists tend to steer clear from substance dualism, which is seen as a relic of a religious, unenlightened past. Even so, substance dualism still enjoys vigorous support from renowned philosophers like Dean Zimmerman and E.J. Lowe. I'm not going to argue for the truth of either of property dualism or substance dualism. Instead, I will argue that an alleged reason to be a property dualist, if it is a conclusive reason, is also a conclusive reason to be a substance dualist as well.

I have in mind the notorious 'explanatory gap' problem, first put forward by Joseph Levine in a classic (and accessible) paper. Here is the problem, as I understand it. If two things X and Y are identical, it is logically impossible for one to exist without the other -- that is, there is a necessary connection that holds between them, such that in all possible worlds where one exists, the other must also exist. So, if Bruce Wayne is identical to Batman, it is logically impossible for Bruce Wayne to exist without Batman. This doesn't mean that Bruce couldn't possibly have refrained from becoming a masked vigilante, but that the person Batman can't exist unless the person Bruce Wayne also exists, since they are the same person. But in such cases, it seems that we are owed an explanation as to why the necessary connection holds. After all, it is very striking that two things should be necessarily linked in this way. To truly understand the identity relation between X and Y, we need an answer to the question, 'by virtue of what are X and Y identical?'. This is easily done with Batman and Bruce Wayne: they are identical by virtue of the fact that they have precisely the same origin, i.e. they are the result of the same particular fertilization event, involving the same particular sperm-and-egg combination. Once you accept the latter story, it becomes impossible to even conceive of Batman existing without Bruce Wayne, or vice versa. The fact about their origins entails, and thus fully explains the necessary connection that holds between them. When it comes to conscious states, things aren't so encouraging. Take the particular pain state which I am now in, and C-fibre stimulation, a particular neurochemical state that exists at the same time as my pain state. Opponents of dualism want to argue that the pain state is identical to the neurochemical state, rather than, say, the neurochemical state causing the pain. But then, as with Batman and Bruce Wayne, we are owed an explanation as to why a necessary connection holds between the neurochemical state and the pain state. But, in contrast to Batman and Bruce Wayne, no such explanation exists. No matter how much we know about C-fibre stimulation, we cannot understand why it is that the existence of my pain state must necessarily follow from my neurochemical state. In this case -- and again, no matter how much neurochemical knowledge we acquire -- it is perfectly possible to conceive of my particular neurochemical state existing without my pain state. For example, I can conceive of my particular neurochemical state existing with a very different kind of conscious state, or with no conscious states at all. Thus, the necessary connection between the neurochemical state and the conscious state remains unexplained: this is the explanatory gap. Levine concludes that the identification of conscious (or 'phenomenal') properties with neurochemical ones is "unintelligible", and many dualists have argued that this unintelligibility problem is conclusive reason to adopt property dualism. Now consider an analogous argument concerning the identification of the self with, say, the brain (the argument could also apply to the identification of the self with the living body):

(1) The identity of my self and my brain would be unintelligible.

(2) If the identity my self and my brain would be unintelligible, I have a conclusive reason to deny the identity of my self with my brain.

(3) Therefore, I have a conclusive reason to deny the identity of my self with my brain.

Premise (1) is true for the same reasons given with respect to conscious and neurochemical properties: there is no explanation as to why a necessary connection holds between the brain and the self. No matter how much we know about brains, we would still be able to conceive of a brain existing without a self, i.e. an entity capable of conscious experience. Hence, we have no answer to the question, 'by virtue of what are my brain and my self identical?' Property dualists must apparently also accept premise (2). If the lack of explanation for the identity between mental and neurochemical properties is enough to motivate the rejection of this identity-claim, it is difficult to see why the lack of explanation for the identity between the self and the brain is not enough to motivate the rejection of this identity-claim. (1) and (2) jointly entail (3), so it looks as though consistent property dualists must accept (3). But, if I am right in thinking that the same kind of argument would apply to the identification of the self with the living body, or with anything other than the self, then it seems that property dualists are committed to substance dualism as well -- unless they can point out a relevant disanalogy between selves and mental properties. If property dualism does in effect 'lead' to substance dualism in this way, this would be good news to substance dualists, but perhaps not so good news for those property dualists who don't wish to be associated with such a fringe, 'wacky' position.

From theism to idealism

One of the joys that come with studying philosophy is that it inevitably involves becoming acquainted with the wackiest theories about the world. Of course, this has its disadvantages: someone outside philosophy, upon taking a quick glance at whatever book or paper you are currently working on, would be bewildered to read about zombies in what purports to be a serious academic piece (I speak from experience). This does little to improve the discipline’s reputation in academia at large, let alone wider society. Oh well.

As philosophical theories go, idealism surely ranks among the wackiest. An easy way to understand idealism is to contrast it to dualism and materialism. Dualism, in its traditional form, holds that there are, at bottom, two fundamental sorts of thing, namely, mind and matter. Materialism, on the other hand, holds that there is only one fundamental sort of thing, and that is matter – minds and mental states are either identical to or constituted by material things and states. Idealists agree with materialists that there is only one fundamental sort of thing, but claim, shockingly, that this thing is mind.

Idealism is most commonly associated with the thought of George Berkeley, the notorious Early Modern bishop and proponent of 'immaterialism'. Berkeley was reacting against the standard view of his day, according to which our mental experiences are caused by mind-independent material objects. Thus, my experience of my desk is caused by my mind-independent, material desk which, importantly, exists regardless of whether or not I experience it. Conversely, Berkeley's immaterialism dictates that my desk ‘exists’ while I don’t perceive it (and no one else perceives it), but only in a very loose sense:

“Bodies (…) do exist when not perceived but this existence is not actual. When I say a [body] exists no more is meant than that if in the light I open my eyes and look that way I shall see it” (Philosophical Commentaries 293a).

M.R. Ayers (1975, p.xii) takes this to roughly mean that ‘My desk exists’ is a short and inexact way of saying that ‘my desk would exist if someone were looking at it’. Here, my desk is not some material entity existing independently of experience. Rather, its existence depends on its being experienced by us. On this view, ‘material’ objects like desks are similar to sensations like pains, which cannot meaningfully be said to exist without being experienced. Material objects, construed as independent of experience, hence do not exist.

Berkeley famously argues for immaterialism on the basis that it is impossible to conceive of an unperceived material object, say, an unperceived desk. Try all you can, Berkeley tells us, you will not be able to imagine a desk without imagining it as perceived. Interestingly, Berkeley’s immaterialism is supposed to form the basis of an argument for the existence of God. The mental stuff that we call ‘experience’ has got to come from somewhere, and there must be an explanation for its stability and rich complexity. A stable and complex system of material objects is ruled out. Hence, a supreme, benevolent mind that sustains our experiences and ensures that their stability (e.g. that I experience the table whenever I turn towards it) seems a good candidate explanatory hypothesis. Arguments from idealism to theism have been taken up in more recent times (e.g. John Foster 2008).

However, the argument that interests me for today’s purposes is, instead, an argument from theism to idealism. This argument also has its roots in Berkeley:

“How can you suppose that an all-perfect Spirit, on whose will all things absolutely and immediately depend, would need an instrument in his operations, or that he would use one if he didn’t need it? Thus, it seems to me, you have to admit that it would be incompatible with the infinite perfection of God for him to use a lifeless inactive instrument such as matter is supposed to be.” (Dialogues, 34).

Berkeley seems to be relying on a principle of parsimony, more popularly known as Ockham’s Razor, which states that ‘we should not multiply entities beyond necessity’. That is, we should no postulate a new kind of entity if it doesn’t help us to explain anything, unless there is some other reason to postulate it.

Suppose that God already exists in our worldview. Obviously, we can’t deny the existence of our experience, with all its complexity and stability. Is there any need to postulate mind-independent material objects in order to explain the existence and character of such experience? No, says Berkeley, because God’s creative activity can carry out this explanatory work, without recourse to a “lifeless, inactive instrument such as matter”. In fact, Berkeley argues, a perfect being such as God would not make use of an instrument which He didn’t need. Thus, positing matter on top of experience and God is at best unnecessary, and at worst incoherent with divine perfection.

A very natural response here is to say that the absence of material things makes God out to be a deceiver, much like Descartes’ ‘evil demon’. After all, it sure looks like there are material beings like chairs, desks and trees. Would a perfect God make the world look material when it isn’t? But Berkeley can easily respond that our belief in material beings is our fault, not God’s, for jumping to conclusions about the causes of our experiences. If we were more careful, we would correctly conclude that material beings don’t exist (in the words of a famous Bengali polymath, ‘we read the world wrong and say that it deceives us’).

This problem, I think, is an excellent opportunity for Christians to check whether we have a solid, biblically-grounded theology of creation. If we do, we will easily spot the error in Berkeley’s crucial description of matter as a needless, “lifeless, inactive instrument”. Berkeley assumes that the material world’s value, if it has any at all, would be as a tool for causing the existence and character of our experience. Not so for Scripture. Genesis has God creating the natural world and declaring it to be good, well before humans even enter the picture. The final act of the book of Job (38-41) has God poetically confront Job with his utter finitude and insignificance relative to the cosmos. Fascinatingly, in describing the wonders of the natural world, God repeatedly insists that Job, as a human, has not seen such wonders:

" Where were you when I laid the earth’s foundation?

“Have you journeyed to the springs of the sea or walked in the recesses of the deep? "Have the gates of death been shown to you? Have you seen the gates of the deepest darkness?

" Have you entered the storehouses of the snow or seen the storehouses of the hail?

The list goes on. One cannot escape the sense that, in this passage, the natural world has a life of its own, independently of Job's experience. Certainly, idealists like John Foster are right in saying that this world is a 'world for us' (2008, see link above), but it is more than that. The natural world has value in its own right, as a divine work of art only partially perceived by us humans. This, I think, is the proper response of anyone well acquainted with Scripture's account of creation -- to say nothing of its doctrine of the incarnation, which has God literally become decidedly material flesh. If we see this, we will not be perplexed by the specter of idealism, or speechless when asked why God would create dinosaurs long before humans were around to perceive them (again, I speak from experience). Berkeley, G., & Ayers, M.R. (1975). Philosophical works. London: Dent.