Imagining zombies

Understanding the relationship between the mind and the body remains one of the most vexed problems in philosophy, cognitive science, and neuroscience. Throughout much of the last hundred years, physicalism has been the orthodox position in the philosophy of mind. Physicalist views share the characteristic attitude that mental phenomena — such as beliefs, desires, experiences and emotions — are either nothing but physical phenomena — brain states, say — or are in some important sense accounted for or made real by physical phenomena.

Physicalism has not reigned unchallenged, however. A number of arguments have been raised which promote dualism in its place — the view that fundamentally, the mind and body are separate, and mental phenomena can never be adequately characterised in terms of physical goings-on.

Perhaps the most prominent and widely discussed of these is the ‘Zombie Argument’, developed and defended by David Chalmers over the past twenty-five years or so — although the line of thought behind it goes back at least as far as Descartes.

Chalmers’ argument focusses on one particular aspect of mental phenomena – phenomenal experience or that-which-it-is-like to undergo a particular mental process or to be in a particular mental state, such as:

“… the felt quality of redness, the experience of dark and light, the quality of depth in a visual field … the sound of a clarinet, the smell of mothballs… bodily sensations from pains to orgasms; mental images that are conjured up internally; the felt quality of emotion … the experience of a stream of conscious thought.” (Chalmers, 2010)

‘Mr Pipo thoughts’, by Nevit Dilmen. CC BY-SA 3.0 via Wikimedia Commons.

In motivating the argument, Chalmers asks us to consider creatures that he calls ‘zombies’ — not these ones! — which are physically identical to human beings but which lack all phenomenal experience. For all the similarity of a zombie’s behaviour to ours, when a zombie peers out into the gradually darkening red-hued sunset; inhales the musty smell of her closet whilst strains of her daughter’s clarinet practice come screeching through the wall; when she cries out wildly due to the touch of a red hot poker, or that of her lover, and so on … there is nothing that it is like to be her. In other words, none of this is accompanied by phenomenal experience.

Zombies may well inhabit zombie worlds; worlds that are complete physical duplicates of our own, but without any phenomenal experiences occurring there. In such a world, for example, your ‘zombie twin’ is currently sat reading about zombies, just as you are, but there is nothing it is like for your zombie twin to do so.

The key to the zombie arguments is the following line of thought: if zombies are possible then physicalism must be false. This is because if all the physical features of a human have been duplicated and there’s still something missing as far as mentality goes, then whatever’s missing can’t be physical: if it were, it wouldn’t be missing! If it can be argued that zombies are possible, then it looks like a good argument against physicalism is in the offing.

The simplest version on Chalmers’s argument runs as follows:

(P1): Zombies are conceivable

(P2): Whatever is conceivable is possible

(C): Zombies are possible

The argument is valid: if the premises (P1) and (P2) are both true, then the conclusion, (C), follows. So any response to the argument ought to target the truth of one of the premises. Typically, those responding to the argument have accepted the first premise, that we can conceive of zombies, but have questioned the second, arguing that whether or not we are able to imagine or conceive of something isn’t a good guide to whether or not that thing is possible.

However, it’s far from clear whether (P1) is in fact true: that is, whether or not we can really conceive of zombies. To see why, it’s easiest to consider some related things we clearly can conceive of, but which don’t live up to the aspirations of (P1). For instance, we can form a picture a human being in our heads, and say to ourselves ‘and it doesn’t have any phenomenal experience’. But this is far from conceiving of an exact physical duplicate of a human which lacks phenomenal experience.

Here’s an analogy, think of a mechanical clock, indeed, an exact duplicate of a mechanical clock you’re acquainted with. Can you conceive of the duplicate’s hands running anti-clockwise, rather than clockwise, or not running at all? You certainly could form a mental picture of the clock and say ‘and the hands run backwards’. But under close inspection, it’s not clear one could maintain this picture under scrutiny without making some change to the clock — say by rearranging the gears, or changing the direction of the motion imparted by the motor.

Additional pressure can be put on the notion of conceivability when one realises that things which are conceivable individually aren’t always conceivable in combination. Think about the following mathematical case: Goldblach’s conjecture says that every even integer greater than 2 can be expressed as the sum of two primes. Whilst we know the conjecture holds up to very large numbers, it remains unproven: given all our evidence, it could be true or it could be false. So it seems that individually, we can conceive of Goldblach’s conjecture either being true or of it being false: but we can’t conceive of both together, of its being both true and false. The contradiction here is obvious.

What about the zombie case? Well, it’s clear we can conceive of the notion of ‘an exact duplicate of a human being’, and, separately, of the notion of ‘lacking phenomenal experience’. Conjoining the two doesn’t lead to an obvious contradiction, like in the Goldblach case. But it is far from obvious, given our relative lack of knowledge of the relationship between the mind and the body, whether or not a contradiction lies waiting to be unearthed in the notion of zombie. Without further information on the nature of the brain, of mentality, and of the sorts of features we take to typify each, assent to (P1) should be withheld.

Featured image credit: ‘Scary Landscape Reflections’, by Leon Fishman. CC BY 2.0 via Flickr.

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