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After reading Wesley’s post about the Penn biologist that that human free will is fiction, my first thought was, “Maybe Dr. Cashmore is a zombie.”

It’s not as bizarre an assumption as you might think (actually it is as bizarre, just not in the way you imagine). The zombies I’m thinking about aren’t like the types found in horror movies such as 28 Days Later or Dawn of the Dead and they don’t (as far as I know) eat people’s brains. These zombies , as they are defined in the field of philosophy, are beings that behave like us and may share our functional organization and even, perhaps, our neurophysiological makeup without ever having conscious experiences.

So defined, zombies are rather tricky. You can’t tell by looking at someone whether they are a normal sentient person or an unconscious creature. It also does no good to directly ask them. Some people who are not zombies will claim they are simply because they are eccentric. And some zombies will claim they are conscious people even though they will deny the attributes necessary for consciousness.

There is, however, one reliable feature that might be useful. Zombies (especially the ones that work at universities and claim to be conscious human beings) appear to have a peculiar attachment to physicalism or materialism, the idea that everything that exists is, in some sense, physical and that nothing nonphysical exists at all. These odd creatures generally come in two basic forms:

Epiphenomenalist zombies believe that mental events are caused by physical events in the brain, but have no effects upon any physical events.

Eliminativist zombies claim that our ordinary, common-sense understanding of the mind is deeply wrong and that some or all of the mental states posited by common-sense do not actually exist.

The eliminativist perspective is the easiest to dismiss since it is inherently self-refuting. For example, one of the claims made by these types of zombies is that it is impossible to make an assertion about anything. This leads to the question of how it is possible to make an assertion that it is impossible to make an assertion? The eliminativist will say that while it is true that they are making such an assertion, it really has no meaning since assertions can’t be made.

As you might imagine, these zombies aren’t taken too seriously. Unfortunately, most other zombies do not realize that when they say that science will one day be able to prove (or at least explain) how consciousness is purely physical, this is what they are talking about. This puts them in the rather peculiar position of claiming that science will one day present a hypothesis that hypotheses don’t exist.

The other, more common variety of zombie is the epiphenomenalist. They are the types that claim that emergent properties (such as the mind) arise out of more fundamental entities (the physical body) and yet are novel or irreducible with respect to them. In essence their argument is that when the right physical properties are combined just so , a new, completely distinct, nonphysical property emerges. (Think of it as a “God did it” explanation with matter filling in for God.)

To restate this idea in a another form, we can say that from a complex physical system P (i.e., P is a human body) arises an emergent property or substance M (i.e., M is the human mind). According to the argument, matter alone does not have the ability to produce M unless it is arranged in the form of P . (This is merely a complicated way of saying that matter can’t “think” unless it is formed into a brain.)

So far there’s nothing that most non-zombies would necessarily find disputable. The controversial assumption, however, is not so much whether P can cause M but whether events that originate in M can cause events in P .

Here’s an example of what I mean: Imagine that after touching a glowing red spot on an electric stove and burning my hand, I form a belief that touching a stove will burn me. In the future, this belief causes me to pull back my hand when I get close to a hot stove.

What has happened is that a physical event in P (getting burned) causes an event in M (my mind feels pain). M produces an M event (a belief that anytime I touch a hot stove I will get burned) that causes P* (an automatic reaction in which I pull my hand back anytime I get close to a stove).

We can put this in diagram form as follows:


| |

P P*

The epiphenomenalist, though, will disagree with my claim. Since, in their view, mental events are caused by physical events in the brain, but have no effects upon any physical events, my belief could not have affected my behavior.

Instead my behavior is caused by muscles that contract upon receiving neural impulses, and neural impulses are generated by input from other neurons or from sense organs. Or something like that. The important part, in the epiphenomenalist view, is that my mental events played no causal role in this process.

Their position could be diagrammed as follows:

M M*

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P —> P*

My brain ( P ) produces my mind ( M ) but my reaction ( P* ) is not caused by a mental event ( M* ).

In our example, event M* would be considered a supra-natural, preternatural, or even supernatural event. (Because of the connotation associated with supernatural, I recommend we use supra-natural.) But, according to our zombie neighbors, there are no supra-natural events, only physical ones. This leads to what philosopher Todd C. Moody calls conscious inessentialism :

Conscious inessentialism clearly entails that any given behaviour could also occur without conscious accompaniments. The only reason why one would suppose that certain behaviours do require conscious accompaniments is that the behaviours in question appear to require mental activity of some sort. Since conscious inessentialism tells us that no mental activity requires conscious accompaniments, it follows that no overt behaviour requires them either. So if conscious inessentialism is true, zombies are possible. Indeed, if conscious inessentialism is true, it is quite possible for an entire world of zombies to evolve, which is the premise of the current thought experiment. It is behaviours, after all, and not subjective states, that are subjected to evolutionary selection pressures. If those behaviours do not require consciousness, then evolution is indifferent to it. That the zombie problem may have significant metaphysical implications is concluded by Robert Kirk in a paper on the topic: `it is hard to see how any intelligible version of Materialism could be reconciled with the logical possibility of Zombies, given that we are sentient’.

But is our neighbor actually a sentient being or a zombie? If conscious inessentialism is true, then it’s possible that sentient beings could have a zombie twin. Their twin would be exactly like them in every respect (physically and behaviorally) except for one aspect: they would not be conscious. It’s also possible that zombie twins may have a propensity to kill their sentient counterpart, hide their body, and assume their life, without anyone being able to tell the difference.

I have to confess that the idea of non-sentient beings living in my neighborhood kind of creeps me out. No doubt they are decent creatures, but I’d still like to know the truth about my neighbors. That’s why I’ve devised a test to help determine the probability that a person is a sentient being rather than a physical, behavior-driven drone.

Starting from myself, I can establish a number of relevant criteria. I know that I have a mind because I use it to think (albeit rather poorly) and to form beliefs. I also know that since my beliefs can affect my behavior, that my mind is distinct from my physical body.

On this point I am either right or I am wrong. If I am wrong then I am unable to tell if I myself am a zombie and the test is moot since everyone could—and most likely would—be zombies also. If I am right, though, I can assume that other minds would function like mine since, as most philosophers concede, the problem of “other minds” can only be solved by analogy.

Other people, who truthfully claim that they believe mental events can cause physical events, would have minds that function much the same as mine. It’s the people that deny this claim, though, that are suspect. If they claim that the only events that can exist are physical events then there is no way to distinguish them from their zombie twins. Their behavior would be identical in every respect and they would both claim to truthfully believe that mental events do not cause physical events. Consistency would also require them to admit that consciousness really wouldn’t matter anyway; they would be, with respect to all relevant functions, just like zombies.

This leads us to conclude, as a reasonable hypothesis, that anyone who claims to believe in materialism is either a zombie twin or a person who believes in zombie functionalism. We are not only unable to tell the difference, we can’t really know why such a difference would matter. Sure they may not try to eat our brains. But you never know when they might try to eat our qualia .

Note: My use of the term zombie is similar to but not exactly the same as the way it is used in the philosophical literature. Most uses of the term refer to the potential existence of such creatures in other worlds. Admittedly, the fact that people with PhD’s write academic papers on whether zombies can exist is quite amusing. But few would go so far as to suggest, as I do, that our neighbors could be zombies.

Some philosophers do use zombies as an argument against materialism :

The general structure of the zombist’s argument is, as follows:

(1) Zombies are possible.

(2) If zombies are possible then materialism fails.

(C0) Therefore, materialism fails.

It’s that simple. Clearly, the materialist is embarrassed by this argument. It is not that he cannot answer to the zombist’s challenge. He has even more than one objection to it. Still, the zombist has the upper hand in this game: He can offer an easily comprehensible and appealing idea (and we all like simple but powerful ideas) and the only thing the materialist can do is-as it seems-to hover on the details.

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