| Thinking hard, or|
|Major trains of thought|
|The good, the bad|
and the brain fart
|Come to think of it|
A philosophical zombie or p-zombie is a hypothetical being that is physically indistinguishable from a human being, but lacks certain qualities such as a soul or qualia that separate it from "real" humans.
The concept of a machine acting like a human being without having consciousness dates back to Rene Descartes. The term "zombie" within a philosophical context was introduced by Robert Kirk in 1975, and made popular by Daniel Dennett in 1991. Eventually, the term "zombie" was expanded to "philosophical zombie", to distinguish the philosophical concept from the zombies of the Haitian voodoo tradition or the zombies from monster movies. This was then abbreviated to "p-zombie".
There are several different kinds of p-zombies, depending on how they are indistinguishable from humans and what specific human quality they lack.
- A p-zombie might just be behaviorally indistinguishable from a human being. Dissecting such a zombie, we might find that it differs completely from a real human being.
- A p-zombie might be functionally equivalent with human beings. That is, such a p-zombie might have a brain made of wires and transistors, but those wires and transistors would correspond to the axons and neurons of a human brain, and it would be possible to map one to the other.
- A p-zombie may be in every way equivalent to a human being, but only be simulating the exact way a human would react without consciously experiencing events.
- A p-zombie might also be physically identical with a human being. Assuming that such a p-zombie is different from a human being would require some kind of dualism or idealism.
Furthermore, there are several different qualities a p-zombie might lack. Often, a p-zombie is assumed to lack qualia, but other possible qualities are intentionality, free will, consciousness, or a soul.
The usual objection to p-zombies as an argument for dualism is that the concept does not make sense without assuming dualism in the first place, thus the idea is begging the question. Effectively, it is saying that a p-zombie is exactly identical to a human except that it lacks a soul - therefore the soul exists. Such an argument is logically valid, but it is vacuous - it tells us nothing.
It does form an interesting enough thought experiment, though, where you can ask how you'd tell them apart from "real" humans, eventually extending to how you can tell that you, yes you, aren't a p-zombie at all. Indeed, if there is no answer, then the soul is unfalsifiable by the limits imposed on it by this thought experiment itself and so doesn't exist or have any bearing on our lives in any meaningful way - belief in it wouldn't even be trivial. If, on the other hand, an observable difference was proposed, the soul would cease to be supernatural, and again, the thought experiment that set out to prove the soul exists in fact disproves it, or at least certain attributes of it.
The other objection is against the conceptual existence of p-zombies, as thinking you can conceive of something doesn't mean the universe gives a shit. Religious apologists have tried that one already.
It has also been pointed out that the arguments in favor of p-zombies are eerily similar to those used in order to justify slavery and oppression in eras past. In the future the philosophical zombie argument could be uncritically applied to any robot even if one would otherwise have to conclude it was even more intelligent, sentient, and conscious than your typical human (some science fiction explores exactly this).
The concept of a p-zombie is a two-edged sword: if it is possible to show that p-zombies can exist, then the theory of eliminative materialism is in trouble, since it would seem that there are phenomena which can't be reduced to strictly materialistic causes. Proving that p-zombies can exist is impossible unless we can define them. Could an entity lacking consciousness be indistinguishable in all material respects from a conscious human being? Since we do not know what causes consciousness all we can say is that given the present level of scientific knowledge an unconscious p-zombies might (or might not) be physically indistinguishable from a conscious human being in all material respects. There appears to be a confusion between detectable differences and actual differences. If consciousness has a material basis there are certainly material differences between conscious and unconscious beings regardless of whether or not scientists can detect these differences.
On the other hand, p-zombies can be used to attempt to show that several concepts like the irreducibility of qualia don't make sense, since they would allow the existence of p-zombies, without any means to distinguish them from ordinary people. Some have even argued that it then would be impossible to know if oneself is or is not a p-zombie. The third type of p-zombie, indeed, might be indistinguishable by any means, considering that there is no physical evidence for the existence of a soul.
 See also
- The p-zombie movie, LessWrong - "I'm Daniel Dennett, bitches!"
- The zombification of philosophy (of mind), Massimo Pigliucci