In the copious literature about consciousness produced by philosophers in the past fifteen or twenty years we find mention of zombies. A philosophical zombie (as opposed to the slow-witted, bloody, undead ones in the movies who like to eat people) is a hypothetical creature used in thought experiments to elucidate what consciousness is. It is supposed to look and act just like a human being but lack subjective experience. David Chalmers defines it thus: “A zombie is physically identical to a normal human being, but completely lacks conscious experience. Zombies look and behave like the conscious beings that we know and love, but ‘all is dark inside.’ There is nothing it is like to be a zombie.”(1) As Philip Goff describes it,
A philosophical zombie version of you would walk and talk and in general act just like you. If you stick a knife into it, it’ll scream and try to get away. If you give it a cup of tea it’ll sip it with a smile. It uses its five senses to negotiate the world around it just as you do. And the reason it behaves just like you is that the physical workings of its brain are indiscernible from the physical workings of your own brain. If a brain scientist cut open the heads of you and your zombie twin and poked around inside, she would be unable to tell the two apart.
However, your zombie twin has no inner experience: there is nothing that it’s like to be your zombie twin. Its screaming and running away when stabbed isn’t accompanied by a feeling of pain. Its smiles are not accompanied by any feeling of pleasure. Its negotiation of its environment does not involve a visual or auditory experience of that environment. Your zombie twin is just a complex automaton mechanically set up to behave just like you. The lights are on but nobody’s home.(2)
Sounds a bit ridiculous, right? Why would somebody postulate such thing? They do so in order to refute the idea that everything is at root physical, that conscious experience is nothing but brain cells firing in certain ways. The notion of a philosophical zombie is a weapon in one of the skirmishes of the ongoing mind-body debate. If we can conceive of such a thing as a philosophical zombie, the opponents of physicalism say, then physicalism must be false. Here is the reasoning:
- According to physicalism, all that exists in our world (including consciousness) is physical.
- Thus, if physicalism is true, a logically possible world in which all physical facts are the same as those of the actual world must contain everything that exists in our actual world. In particular, conscious experience must exist in such a possible world.
- In fact we can conceive of a world physically indistinguishable from our world but in which there is no consciousness (a zombie world). From this (so Chalmers argues) it follows that such a world is logically possible.
- Therefore, physicalism is false. The conclusion follows from 2 and 3 by modus tollens.(3)
This chain of thought has provoked lots of heat but little light. Can we really conceive of a philosophical zombie or do we only think we conceive of it? If we only think we conceive of it, isn’t that conceiving of it? If we can conceive of it, does that make it logically possible? Does logical possibility have any bearing on what actually exists? Is the concept self-contradictory? Is the argument circular, assuming as a hidden premise what is to be proved? The questions go on and on. That they can’t be answered should serve as a clue that there is something out of whack in the very foundations of the controversy.
In fact the bickering about zombies is a red herring, a distraction that serves no purpose. The philosophical concept of zombie is not only ridiculous but meaningless. By definition such a zombie is an exact physical duplicate of a human being that acts exactly the same as a human being. Hence, there is no possible way for anyone to distinguish a zombie from a human being. As William James says, “What difference would it practically make to any one if this notion rather than that notion were true? If no practical difference whatever can be traced, then the alternatives mean practically the same thing, and all dispute is idle.”(4) There is no practical difference between saying that someone is a zombie and saying that someone is a human being, so the distinction is meaningless. The concept of zombie is completely useless.
The distinction between zombie and human being seems to be reasonable only because we mistake experience of subjective (private, internal) objects and events for experience of objective (public, external) objects and events. In both cases we are conscious of something. Because more than one person can be conscious of something objective, we mistakenly act as if more than one person could be conscious of something subjective. But they can’t. Only one person can be conscious of something subjective, namely the person whose subjectivity it is. We act as if positing an entity that is just like a human being but lacking consciousness is like positing an entity that is just like an able-bodied person but lacking an arm. The two are not at all similar, and it is a kind of category mistake to treat them as if they were.
Because the concept of philosophical zombie is meaningless, it has no bearing on the question of how mind and matter are related. We’d all be better off if we quit wasting our time in idle disputes about it.
(1) Chalmers, “Zombies on the web.”
(2) Goff, “The Zombie Threat to a Science of Mind,” p. 6.
(3) Wikipedia, “Philosophical zombie.”
(4) James, “What Pragmatism Means,” p.42.
Chalmers, David. “Zombies on the web.” Online publication http://consc.net/zombies.html as of 21 August 2013.
Goff, Philip. “The Zombie Threat to a Science of Mind.” Philosophy Now magazine, #96, pp. 6-7.
James, William. “What Pragmatism Means.” Pragmatism and four essays from The Meaning of Truth, pp. 41-62. New York: Meridian Books, 1955. Online publication http://www.marxists.org/reference/subject/philosophy/works/us/james.htm as of 21 August 2013.
Wikipedia. “Philosophical zombie.” Online publication http://en.wikipedia.org/wiki/Philosophical_zombie as of 21 August 2013.