Fashions change. The problem of consciousness, once banned from serious consideration by psychologists, is again high on the agenda. Yet typically researchers are looking under the lamp that currently shines brightest rather than in the area where the phenomenon went missing. They are identifying consciousness with high level thought processes and seeking to explain it in "thinking machine" terms; but they are largely ignoring bodily feeling.

Yet if we listen to the kinds of questions ordinary people ask - "Are babies conscious?", "Will I be conscious during the operation?", and so on - it is clear that, again and again, the central issue is not thinking but feeling. People's concern is not with the stream of thoughts that may or may not be running through their heads but with the sense they have of being alive at all - which is to say, alive and living in the presence of sensation.

The problem, then, is to explain just what these sensations - conscious sensations - are. We want a theory of why it feels to us as it does to taste salt on our tongues, to look at the blue sky with our eyes, to burn our fingers on the stove. But - and here is what is going to make this problem hard - the theory must not beg the question by assuming any prior acquaintance with what is being explained: namely, sensory consciousness as such.

Lets stipulate, then, that the theory has to be comprehensible to a scientist from Mars - an individual in many ways not unlike ourselves, highly intelligent, perceptive and even capable of self-reflection, but who nonetheless has never evolved into the kind of being who has sensations. Suppose we could explain to this Martian what happens in the brain of a human being who is engaged, say, in smelling a rose. And suppose he could thereby arrive at the entirely novel (to him) conclusion that it must be like something to be this human being, and indeed like this : "I am feeling this thick, sweet, olfactory sensation in my nostrils". It's a tall order; but, still, it's what the theory ought to do.

Is a theory, which could bring this off, a possibility even in principle? Since the theory must employ only such concepts as the Martian can make sense of at the outset, we need to consider what kind of pre-theoretic notions he brings with him. Given that as yet he knows nothing about sensations, will he have other essential concepts on which to build?

We want him to understand that the human being is the subject of sensations. Can we assume he will at least have, to start with, the idea of what it is to be a "subject"? I'd say we can. For presumably the Martian is already himself a subject in the following crucial sense: an autonomous agent who acts in the world. Provided he can take himself as a model, he ought already to have the basic concept of an "I". Then, can we assume he also understands the idea of being the "subject of"something? Again, we can. For, as an "I" who does things with his body, he himself already has this genitive relationship to his own actions: he is the author of everything he does. So, will he even have the idea of being the subject of something with the some of the peculiar properties of sensations: especially, that (i) they belong to the subject, (ii) they implicate part of his body, (iii) they are present tense, (iv) they have a qualitative modality, (v) their properties are phenomenally immediate? In fact he will: for analysis shows that bodily actions already have precisely these characteristics (i) - (v).

Now, this may not seem much as a basis for understanding sensory consciousness. But I believe that, with the right theory, it will be enough. Suppose we suggest the following theory to the Martian (it is my own theory, but others like it might also do the trick):

When a person smells a rose, he responds to what's happening at his nostrils with a "virtual action pattern": one of a set of action patterns that originated far back in evolutionary history as evaluative responses to various kinds of stimulation at the body surface - wriggles of acceptance or rejection. In modern human beings these responses are still directed to the site of stimulation, and still retain vestiges of their original function and hedonic tone; but today, instead of carrying through into overt behaviour, they have become closed off within internal circuits in the brain; in fact the efferent signals now project only as far as sensory cortex, where they interact with the incoming signals from the sense organs to create, momentarily, a self-entangling, recursive, loop. The theory is that the person's sensation, the way he represents what's happening to him and how he feels about it, comes through monitoring his own signals for the action pattern - as extended, by this recursion, into the "thick moment" of the conscious present.

Then, how will the Martian understand this? Presumably nothing in his own direct experience corresponds to what we have just described to him. But, still, he should be able to work it out. He will be able to grasp the key fact that sensation consists in monitoring commands for action in response to stimulation. He will be able to appreciate the peculiar features of the action pattern that has in fact evolved. And so he'll be able to work out that if a subject like himself were to get involved in doing what the human being is doing, the result would be that he would have just these beliefs about it, these attitudes, these things to say, these that he can't say, and so on - in short he would experience it like this.

But if the Martian can work all this out from the theory, would this mean he actually acquires first-hand experience of sensations in the process? No: no more than someone who works out from physics and chemistry that H2 0 constitutes water gets wet. A theory of consciousness is not a way of conferring consciousness; it is a way of understanding why consciousness-generating brain states have the effects on people's minds they do. In fact the Martian himself may have no sense organ with which to smell the rose at all: and yet, if the theory is right, he should still be able to discover all that we ourselves can discover by direct acquaintance. (And one day, of course, when we get to study Martians, the boot may be on the other foot).


Humphrey, N. (1992). A History of the Mind.

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