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The Mark of Zombie

These days philosophers of mind talk a lot about zombies, to illustrate ideas about the nature of consciousness. Edward Ingram thinks they are all crazy.

As every intelligent person knows, things which exist are of two sorts. The first sort is conscious things – things like you and me, cats and dogs, and chimpanzees and tigers. These things, the conscious things, have experiences: they experience the redness of red, the paininess of pain, the yumminess of yum, and so on. Philosophers call these experiences qualia. Qualia, by definition, are the sole preserve of conscious things.

The second sort of thing that exists is zombies. Zombies are the same as conscious things, save that they lack consciousness. Tables are zombies, so are pocket calculators, and so are microwave ovens. Kick a microwave oven and it doesn’t feel pain. There is, as the saying goes, nothing it is like to be a zombie, and microwave ovens are zombies.

Now, it is admitted that there are difficulties with the distinction between zombies and non-zombies. Philosophers are uncertain whether bees are zombies, for instance. Likewise, although all admit that consciousness is manufactured by brains, they also admit that the constituent parts of brains – neurons – are themselves zombies. Nonetheless, philosophers, being sensible people, brush these difficulties aside. After all, microwave ovens are zombies and people are ‘people’. Only a madman would suggest otherwise.

First Fantasy

The astronauts discovered Twin Earth, a planet indistinguishable from Earth. Thus on Twin Earth there was a twin America, a twin Atlantic Ocean, a twin London, even a twin Buckingham Palace. The astronauts were intrigued by this, and by the fact that the inhabitants of Twin Earth spoke the same languages as ordinary Earth people (twin English, twin Chinese, etc.).

In time, however, the astronauts made a discovery which was stranger still. Through archeological research, they discovered that, years back in Twin Earth’s past, a team of malicious aliens had sprinkled zombie poison over the planet. This had had the effect that, although life on Twin Earth had evolved in exactly the same way as had life on real Earth – there had been a twin Cambrian explosion, a twin dinosaur extinction, a twin rise of the mammals, and so on – every living creature on Twin Earth was a zombie (zombie poison, you see, is indestructible, has instantaneous effects, has no antidote, and hangs around forever).

Of course, this zombie poison changed the behaviour of the living beings on Twin Earth not one jot. The (zombie) cats and dogs on Twin Earth mewed and barked just like the (nonzombie) cats and dogs on real Earth, and likewise the people on Twin Earth spoke in the same way as Earth people. It was just that when the Twin Earthers spoke of ‘inner events’ – of dreams for instance – they didn’t mean quite the same things by them as did ordinary Earth people.

Naturally, the astronauts found all this intriguing. However, one day an awful thought came to them: zombie poison is indestructible, so they, the astronauts, should be infected. And blood tests confirmed this. The astronauts were zombies!

To this, the Twin Earth zombies noted that the situation was fascinating. You see, how can zombies know that they are zombies?

Second Fantasy

The (zombie) astronauts zdecided to return to Earth (note: when a normal individual decides, it decides; when a zombie decides, it zdecides, and so forth) in the zhope that Earth’s scientists could find a cure for their condition. Upon their arrival, having placed themselves in the strictest quarantine, they told the scientists of their zplight, and the scientists set about developing a remedy.

This raised a tricky problem. You see, the scientists weren’t sure, even if they could find a cure, how they could know it was a cure. After all, if a man who is a zombie first tells you he is a zombie, and then, later, tells you he is not a zombie, how do you know he is conscious as opposed to just zthinking he is conscious? Does there exist a ‘mark of zombie’?

To this end, the scientists developed a machine, a consciousness meter. And it proved effective. When the scientists held it to their heads, it registered “very conscious”; when they tried it on a cat, it registered “conscious”; and when they tried it on a spider, it registered “dimly conscious”. But when they tried it on the astronauts, sure enough, for each one it registered “complete zombie”.

Now, scans had revealed every cell in the astronauts’ bodies to be infected with the zombie poison. So there was nothing for it but to rebuild the astronauts’ bodies, and memories, from scratch. The scientists did this with the help of their most powerful computer. Their approach, for each astronaut, was this:

First, for every neuron within the astronaut’s head, the computer calculated (a) what the neuron was doing, and (b) what it would have been doing had the the zombie poison not been present. This done, the brain, complete with memories, was rebuilt – each neuron being replaced with a functionally equivalent nanocomputer. Next, through advanced cloning and rapid growth techniques, a new body was grown in a basin of nutrient. When fully grown, the clone’s brain was replaced with the nanocomputer brain and disposed of. Finally, the old body was incinerated and (for extra safety) the ashes shot into outer space.

So, the day came when the astronauts were to be switched back on. And it worked! The consciousness meter, upon being applied to each of the ‘new’ astronauts, registered “very conscious”, just as had been hoped. And the astronauts asserted how grateful they were to be back to normal again, how [z]horrible it had been to be a zombie (this puzzled the scientists), and how [z]anxious they had been lest the treatment fail (this puzzled the scientists even more).

However, the scientists, being mindful of the unprecedented research opportunity, had included, within each astronaut’s nanocomputer brain, a parallel nanocomputer for each of the billions of ‘working’ nanocomputers. These parallel nanocomputers were identical in all respects to the working nanocomputers save for two things: first, each was radio-controlled such that it could be placed in active or passive mode; second, each contained the functional equivalent of zombie poison. Now, when in passive mode each of these parallel computers did nothing, but when in active mode it overwrote the activities of its ‘normal’ counterpart. Thus it was that the astronauts could be tuned, one nanocomputer at a time if needs be, to everything from “very conscious” to “complete zombie”. (Indeed, there was a bonus: by tweaking the system the scientists ascertained that they could tune each astronaut up to “hyper-conscious” – this was explained by the fact that, in the normal course of events, each human being is ‘partzombie’, that is, each has a ‘conscious mind’ and an ‘unconscious mind’.) Because of this, the scientists hoped they could pursue fundamental research into zombiedom.

The test began. An astronaut sat in a research booth and, as a scientist turned a dial and thereby flipped millions of parallel nanocomputers into active mode, the consciousness meter registered, first “very conscious”, then “conscious”, then “dimly conscious”, then, finally, “complete zombie”. This achieved, another scientist started an interrogation: “What colour’s this? [pointing to a red square]”, “How does this feel? [kicking the astronaut]”, and “What does this taste like? [pouring vinegar down his throat]”.

“zRed. zOuch! zYuk!” replied the astronaut.

Stage one satisfactorily complete, the first scientist turned the dial up a notch such that the consciousness meter registered “almost a zombie”. Again the second scientist pointed to the red square; again he kicked the astronaut; again he poured vinegar down the astronaut’s throat.

“Pink. Um! Hmm!” came the reply.


Now, doesn’t all this talk of qualia and consciousness and zombies and non-zombies and hyper-consciousness and dim consciousness and conscious minds and unconscious minds strike you as insane?


This article is a compendium of several arguments. You can find out more about the ‘zombie’ debates on which it is based from the following sources:

Chalmers, D. (1996). The Conscious Mind: In Search of a Fundamental Theory. Oxford University Press.
Chalmers developed the ‘fading qualia’ argument, presented in the Second Fantasy, in order to refute denials that machine intelligence is possible.
Dennett, D. (1992). Consciousness Explained. Penguin.
Dennett argues, as is implied by the First Fantasy, that humans are zombies that zthink they are conscious. Also see:
Dennett, D. (1995). ‘The Unimagined Preposterousness of Zombies’. Journal of Consciousness Studies, 2, 4, 322-326.
Flanagan, O., & Polger, T. (1995). ‘Zombies and the Function of Consciousness’. Journal of Consciousness Studies, 2, 4, 313-321.
Flanagan and Polger argue that Twin Earth zombies could acquire ‘ordinary English’. Dennett (1995) argues that they must.
Penrose, R. (1990). The Emperor’s New Mind: Concerning Computers, Minds, and the Laws of Physics. Vintage.
Penrose, as far as I am aware, was the first to use the idea of a consciousness meter.
Poundstone, W. (1991). Labyrinths of Reason: Paradox, Puzzles and the Frailty of Knowledge. Penguin.
Poundstone provides nice discussion on the conceptual problems inherent in the notion of ‘consciousness doubling’, or hyper-consciousness, as implied in the Second Fantasy.
Smullyan, R. (1982). ‘An Unfortunate Dualist’, in D. Hofstadter and D. Dennett The Mind’s I. (pp. 383- 384). Penguin.
Smullyan uses the notion of zombie poison, as do both fantasies, to refute mind/body dualism. The structure of ‘The Mark of Zombie’ closely mirrors that of Smullyan’s paper.

© Edward Ingram 2000

Edward Ingram is Fellow in Philosophy at the School of Psychology at the University of Wales, Bangor.

[The Mark of Zombie is an extract of the author’s book Robots, Zombies, Mind, God, Fuzz, which is nearing completion and is being handled by the author’s agent, Amanda Little of Watson Little Ltd, London]

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