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.

Are you substantial?

Philosophers have traditionally distinguished between substances and attributes. This may seem like yet another piece of obscure philosophical jargon, but is meant to capture the very intuitive distinction between objects and their properties. My pet hamster, Colonel Mustard, is a substance. Colonel Mustard's furriness is one of his attributes. The problem of accounting for the fact that different substances can share attributes has been the subject of several posts on this blog. Another worry has to do with providing a clear criterion for demarcating substances from attributes. At least since Aristotle, a very standard way of doing this involved saying that attributes necessarily depend on things outside of themselves for their existence, while substances do not. The following excerpt from Descartes' Principles of philosophy (I.51) exemplifies this well:

" By substance we can understand nothing other than a thing which exists in such a way as to depend on no other thing for its existence."

The thought here is that attributes, by their very nature, always seem to depend on other things for their existence, namely, the substances that 'have' them. Colonel Mustard's furriness couldn't possibly exist without Colonel Mustard (or, at least, without other furry things). An attribute essentially needs to inhere in a substance in order to exist. A substance, in contrast, is not dependent in this way. Of course, typical substances themselves in fact depend on other substances for their existence -- Colonel Mustard wouldn't survive very long if I stopped feeding him, or if the sun disappeared. Nevertheless, it is perfectly possible to conceive of Colonel Mustard as existing without the sun, or without being fed, though the laws of nature make this impossible in the actual world. In contrast, it is impossible to conceive of 'furriness' existing without something that is furry. Hence, attributes like 'furriness' necessarily depend on other things for their existence, while substances like Colonel Mustard do not.

This way of demarcating substances from attributes accommodates our intuition that objects are in some sense 'more real' than their properties. Colonel Mustard is substantial, he exists in his own right. 'Furriness', at best, is an aspect of him, not fictional, but not substantial either.

The distinction quickly runs into trouble, however, because there is apparently only one being that meets its criterion for substantiality -- God. Indeed, all substances (other than God) are created and sustained in existence by God. Crucially, every substance (again, other than God), if it exists at all, necessarily owes its existence to God. God exists necessarily, and whatever else exists necessarily depends on Him for its existence. This means that while Colonel Mustard's existence may not necessarily depend on the sun, it does necessarily depend on God's creative activity, in the same way that 'furriness' necessarily depends on furry things for its existence. God, on the other hand, being the ultimate and necessary ground of existence, is not similarly dependent (in fact, God is necessarily independent). Descartes recognized this problem, and conceded that, on the standard definition of substance, strictly speaking, God is the only substance. He nonetheless argued that everyday objects could be substances in some attenuated sense, since they are necessarily dependent on God and nothing else, whereas attributes are necessarily dependent on God and on substances (Principles I.51).

A much more radical, if more coherent, response to this puzzle is offered by Baruch Spinoza, who wholeheartedly embraces the conclusion that there is only one substance, God, and that all other alleged substances -- you, me, Colonel Mustard, Donald Trump, etc -- are really just properties or modes of God. You and I don't exist in our own right, we are, at best, aspects of the single divine substance. Steven Nadler puts it nicely in his paraphrase of Spinoza's reply to Descartes:

" In effect, he is saying to Descartes: I agree that a substance is essentially what exists in such a way that it depends on nothing else for its existence; but then, as you yourself admit, strictly speaking only God is a substance; and I, in order to be fully consistent, refuse to concede to finite things even a secondary or deficient kind of substantiality." (2006, p.56)

Hence Spinoza's monism -- there is only one thing, which possesses an infinity of modes. Hence also his pantheism -- everything other than God is an aspect of God, such that God's being 'envelops' everything. This lands us with a rather bizarre theology (it is still debated whether Spinoza's opponents were right in calling him an atheist). More importantly for our purposes, this lands us with an utterly odd picture of ourselves and the objects of the world around us, which, we are told, aren't really objects at all, but properties or 'modes'.

Of course, we can just bite the bullet and accept that we aren't substantial, but instead properties of something else -- God, or whatever else we think to be the ultimate ground of existence. But I tend to think that philosophical systems ought to try to respect the linguistic conventions of wider society. Such conventions stipulate that you, myself, and Colonel Mustard are objects, not mere attributes or properties. As I've said before, philosophers are free to make up their own linguistic conventions, but will have very little to say to those outside philosophy if their use of everyday concepts like 'object' radically differs from that of the wider public. I take it that philosophers should have something illuminating to say to those outside philosophy. Hence, the conclusion that everyday objects aren't substances at all should strike us, I think, as a sure sign that there is something wrong with the argument that inferred it. As we have seen, what brought us to the radical monistic conclusion is the traditional account of the substance-attribute distinction, whereby substances, unlike attributes, are not necessarily depending on anything outside their existence. Thus, if we are to avoid the unacceptable conclusion that you and I are nonsubstantial, it looks like we will have to give up the account. One perhaps surprising upshot of this may be that there is no clear line between substances and attributes. Certainly, different accounts of the distinction can be put forward, but philosophers have struggled to come up with a satisfying alternative (see McBride 2005 for a pessimistic survey of such attempts). But perhaps this shouldn't be surprising after all. The claim that Colonel Mustard isn't a substance or object at all, but rather a mere mode or property of God, may be absurd. But the claim that Colonel Mustard is less substantial than God, but more substantial than 'furriness', isn't obviously absurd.

This is especially true if we take properties to be tropes, i.e. particular things that exist in the objects that have them. If, say, the furriness of Colonel Mustard is a particular 'furriness-trope' that, along with other tropes, helps to constitute Colonel Mustard, then both Colonel Mustard and his furriness are particular, concrete things in the world, and it is easier to imagine how the difference in substantiality might be a matter of degree.

MacBride, F. (2005). The Particular–Universal Distinction: A Dogma of Metaphysics?. Mind, 114(455), pp.565-614. Nadler, S. (2006). Spinoza's Ethics. Cambridge: Cambridge University Press.