In today’s lecture, I want to cover two things: first, modern, more scientifically oriented motivations for rejecting dualism. Second, consciousness, why many philosophers consider it a problem, and why some philosophers think it may provide the basis for a non-Cartesian form of dualism.

I mentioned last lecture that Leibniz worried about Descartes’ dualism on the grounds that it violated conservation of momentum. Conservation of momentum is in just as good of shape today as it was back in Leibniz’s day, but it doesn’t get invoked often. I’m not sure why this is. Maybe, because we’re more used to talking about energy, which takes all kinds of forms, including gravitational potential energy and chemical potential energy and the energy stored within matter that is released in a nuclear blast, and maybe that makes too easy the rebuttal that there might possibly be soul potential energy or some such.

Of course, the idea of soul potential energy sounds kind of crazy once you spell it out, so maybe that’s not the reason we don’t hear conservation arguments against dualism much anymore. Maybe there’s some vague unease with relying too heavily on any one law of physics (before Newton, a lot of people thought action at a distance was impossible, but now we know gravity, the electric force, and the nuclear force all operate at a distance.) Or maybe the fall of conservation arguments is a historical fluke, with no good reason behind it.

Anyway, one starting point for arguing against dualism, based on modern science, is called “the completeness of physics.” According to David Papineau, this principle states that “all physical effects are fully determined by law by prior physical occurrences.”

On this basis, Papineau provides the following argument (this again is a quotation from Papineau):

1) (the completeness of physics): All physical effects are fully determined by law by prior physical occurrences
2) (causal influence): All mental occurrences have physical effects
3) (no universal overdetermination): The physical effects of mental causes are not all overdetermined
Conclusion: Mental occurrences must be identical with physical occurrences.

The first premise is supposed to be the result of scientific inquiry, so I’ll hold off on it and comment on the philosophical basis for the second two premises. The claim that all mental occurrences have physical effects is straightforward seems to be just common sense. I feel hungry, and lo and behold, I go get food, I think about what I want to tell you about the mind body problem in class today, and lo and behold I tell you those things, and so on and so forth. Probably you can think of lots of examples. Our thoughts can lead to actions, that’s just obvious.

But what the heck is “overdetermination”? Overdetermination is when an event have two different causes, and each would be sufficient to determine that the event happen. The example that always gets used is that Sherlock Holmes and his sidekick, Watson, both shoot Holmes’ archnemesis, Moriarty, and their bullets both hit him at the same time and kill him, and either bullet alone would have killed him. From this example, it should be obvious that overdetermination can happen sometimes, but it would be crazy to think its happening all the time. In the case of the mind body problem supposing that our actions are overdetermined by physical and mental events working together would be to suppose that when I’m hungry, my mental process cause me to go get food, and my physical processes also equally cause me to go get food, and if the physical processes failed my mental processes would still do the job, but somehow failures of that sort never, ever, happen, the system is always perfectly coordinated. That sounds just crazy.

These days, a lot of philosophers sort of take physicalism for granted, and even if they don’t say that, they may take the idea of the completeness of physics for granted, saying science has established that physics is complete and leaving it at that. The reason I’m using Papineau as my source for physicalism is that he does cover these things.

Papineau gives two main scientific reasons for accepting the completeness of physics. First is the “argument from fundamental forces,” the argument that scientists often describe various forces out there operating in the world, but then they succeed in explaining them in terms of a few fundamental physical forces: gravity, the electric force, the nuclear forces. Second, Papineau argues, scientists have spent a lot of time studying physiology, and they never seem to bump into non-physical causes in physiology. This is the “argument from physiology.” If scientists search and search and search without finding whatever non-physical causes of physical events that there are supposed to be, then where are these non-physical causes? Are they hiding from us?

If you go to the library to look up Papineau’s essay, you’ll get some very interesting history for the scientific advances that Papineau thinks supports physicalism. However, I think he may leave a couple things out, so just to give you one big idea quickly: it seems like we can arrange sciences from low-level to high level sciences, and scientists have had a lot of success explaining sciences in terms off the one below it on the hierarchy. And the bottom of the hierarchy is physics, then you have chemistry, biology, psychology, and the other social sciences, in that order.

Start with physics and chemistry. You may be used to hearing of quantum mechanics as this crazy thing that doesn’t have any relevance under normal circumstances, but scientists have actually worked out that you can explain a lot of chemistry with quantum mechanics, especially chemical bonds. You can’t explain chemical bonding with Newtonian physics. Now, for complicated systems we can’t do the calculations, but a lot of scientists are convinced that in principle, physics could explain all of chemistry.

Move to biology. In high school biology, you probably learned about how the body does its work with large molecules: DNA, RNA, enzymes, and so on. We’re actually coming to understand the functions of a mind-boggling number of biological molecules, more than anyone person could know about, that’s why its so important for science to have many scientists working at many universities to do the kinds of things modern science tries to do. It wouldn’t be surprising if everything in biology were explained by chemistry. Then you have neuroscience, explaining psychology in terms of biology. We can explain the most basic aspects of sensory experience in terms of fine neural circuitry, and for more complicated things we at least know there’s strong connections between what’s going on in the brain and the behavior we associate with psychology.

It’s those kinds of scientific discoveries that make a lot of scientists and philosophers want to be physicalists. In a sense, you could even bypass Papineau’s three-premise argument and just say that science supports physicalism directly. It wouldn’t be a deductive argument, but on Papineau’s statement of the argument, you still end up having to say that science supports the completeness of physics in some non-deductive way.

However, Papineau’s three assumptions gives us a way of classifying ways of rejecting physicalism. (Also, being able to say “the principle of the completeness of physics” is a good way to sound like you know what you’re talking about, but here we’re concerned with alternatives to physicalism.) You can get a different version of dualism for each of the three assumptions you might reject. Descartes would have rejected the completeness of physics premise. The best-known defenders of dualism today, in contrast, people like Jaegwon Kim and especially David Chalmers, reject the causal influence premise: they don’t think all mental occurrences have physical effects. They think some mental occurrences are physical occurrences, and those have physical effects, but some mental occurrences are produced by physical things without causing anything physical. This view is known as epiphenomenalism, a term coined by Thomas Henry Huxley, a.k.a. Darwin’s bull-dog for his defense of evolution, though by the way while Thomas Huxley is a good name to know, I don’t know how similar his views are to those of the contemporary guys we’ll be talking about, and you’ll only be tested on the modern guys.

Modern epiphenomenalists tend to be specifically epiphenomenalists about subjective consious experience. The paradigm case of conscious experience is often given as the redness of red. These subjective conscious experiences are called “quale,” plural “qualia,” another good word for showing off your philosophy knowledge. If you don’t know what that means, I’m not going to try to explain it precisely, but instead hope that it’ll become more clear as I give examples. As an initial illustration of the modern epiphenomenalist view of consciousness: it seems that hunger causes us to eat. Someone like David Chalmers, though, would say this is what’s really happening: your brains gets information about your needing food from your body, and that sets into motion a series of brain events that will hopefully result in you eating, eventually, and will cause you to eat through purely physical means. In a sense, that’s hunger. But the subjective feeling you get of hunger isn’t what causes you to eat. Rather, its a non-physical event that doesn’t cause anything, but it may seem to cause something, because its caused by the very same brain events that cause you to eat.

So, why would you believe something like this? This is pretty clearly a view for people who really like the scientific view of the world, and want to stick to it as much as they possibly can, but for some reason think that consciousness can’t be covered by physicalism. The arguments are similar to Descartes’ arguments, but philosophers today are more careful about what they apply to. Back in Descartes day, it would have been very easy to Descartes, “maybe there in some sense is a mind distinct from the body, but that doesn’t mean all the things you assign to the mind instead of the body really belong to the mind.” As a historical note, Descartes initially claimed his arguments for dualism proved that the soul was immortal, but he backed off this claim, seeing he hadn’t really proved that. Contemporary philosophers tend to be much more careful. I’m going to describe two arguments, maybe not the best ones, I won’t take a position on what the best arguments are, but I’ll give you two argments that are well-known and very memorable, as they involve zombies and super scientists and all that.

Okay, where do zombies come in: in the context of this particular debate, zombie doesn’t mean a slow-moving creature that comes in large numbers at the apocalypse and tries to eat your brain. Zombie just means a being like an ordinary human in every physical respect, but lack consciousness. So they don’t rot, they don’t move slower than normal, they don’t go around moaning “braaaiiins…” They’re even indistinguishable when you test them with electrodes in their brain or under fMRI. It’s just that they don’t ever experience color, or sound, or hunger, or anything like that. If this idea doesn’t make any sense to you, well, not all philosophers agree that it makes sense, but it might be easier to understand if you consider this question: some philosophers have worried about whether other people really have minds. This can’t be a worry about whether people have the ability to behave in the way we associate with minds, because we can see people’s behavior. This must be a worry about something like whether other people really experience colors and sounds and feelings, or whether they’re like robots, managing to respond appropriately without really experiencing the world.

An alternative version of the zombie argument that you may find more attractive is the inverted spectrum argument. This comes from the worry “what if other people see red the way I see green? What my green is other people’s red? What if other people see the world as a photonegative of how I do?” How many people think they understand this worry? I once heard a professor who had been teaching for a long time say about two-thirds of his students tend to get this idea. Okay.

The zombie argument, or inverted spectra argument, starts with the claim just that zombies are possible, or that an inverted spectra is possible without any physical differences. It has to be a real, deep sense of possibility, not just apparent possibility, but nothing more than possibility either.

Then you get this argument:
1) If zombie are possible, consciousness is not physical
2) Zombies are possible
3) Therefore, consciousness is not physical

If you remember the masked man example from last time, you might think contemporary physicalists would reject premise (1). However, most of them don’t think this is analogous to the masked man case. It’s more analogous to this case: since life is physical, you can’t have something that’s exactly physically identical to a living thing, down to the molecular biology, and yet not alive.

Then, the question is whether zombies are possible. Debates over whether zombies are possible tend to get very quick into technical philosophical ideas about what’s really possible, we can talk about that, but I’m not going to burden you with it right now, just a quick check, what do people think? How many people say, “yes, zombies are possible”? How many nos? I myself tend to be kind of skeptical about these off-the-wall possibility claims.

The other argument is the knowledge argument. Based on what I’ve been told about freshmen philosophy students by one of my former professors, I think you may find this argument more attractive. The knowledge argument asks us to imagine a super-scientist named Mary who spent her entire life of getting super-scientist training in an entirely black and white environment, where she never sees the color red (it’s never really addressed why she doesnt’ become acquainted with red through her own body, maybe she’s a black and white mutant, or bleeds green, or just never bleeds, or something.) But she’s a super-scientist, and her specialty is color vision. She knows everything there is to know about what happens in the visual systems of the brain when people see color. But she never becomes acquainted with color directly. Now, imagine one day she is let out into the world and sees a red rose. Does she learn what it’s like to experience red? Does she go from not knowing what it’s like to experience red to knowing what it’s like to experience red?

The argument is that if we accept that she does gain new knowledge, physicalism has to be false, because she knows everything physical about seeing red but doesn’t know what it’s like. This, admittedly, is an argument that sounds more like the masked man case. It involves knowledge, to recall a technical term we learned last time, it involves “intentionality.” But this isn’t just a case about knowing one thing about the physical nature of red but not another thing about the physical nature of red. This is about knowing absolutely everything there is to know about red, in terms of physical perception, but not knowing what it’s like. Its a question of whether physical knowledge and knowing what it’s like overlap.

How do we respond to this argument? I think there are two big ways. One, you could question the thought experiment. Maybe you think a true super-scientist would learn what its like to see red through text book learning alone. Or maybe you just feel unsure, you think without any actual super-scientists, we can’t know whether a superscientist would know what it’s like. The other option, is to conceed Mary would learn something that isn’t knowledge of the physical world, but it isn’t learning something non-physical, but learning in a different way. Maybe she’s gaining acquaintance, or gaining the ability to recognize red, or coming into contact with a previously known fact through new means. Those are the kinds of things physicalists say when they want to resist the knowledge argument.

Final comment: maybe you aren’t totally confident about the zombie argument or the knowledge argument. Maybe you’re confused by all the subtleties. You should be aware that even philosophers who don’t see these as knock-down arguments often begin to suspect that they are getting at something, that philosophers who promote them have picked out a feature of our minds that isn’t readily explained by current scientists. Not saying what that means, ultimately, but it’s worth knowing.

That concludes what I have prepared today–we covered a lot of ground. Questions?

References:
David Papineau, “The Rise of Physicalism,” from /Physicalism and its Discontents/, ed. C. Gillett and B. Loewer. Cambridge, 2001.