Igor Aleksander asks us to take seriously his argument concerning the problem of consciousness, by suspending "the deep contempt that many have for inanimate object" (THES, November 18). Although we are "happy to think of a friend as being conscious", if she were to "unzip the front of her face and reveal a heap of circuit boards and transistors our attribution of consciousness might vanish". This is sheer prejudice on our part, he claims, and in turn results in a "distaste for mechanistic ideas".

The problem with Aleksander's train of thought here is that if I were simply of the opinion that a friend were conscious, and she suddenly unzipped the front of her face and revealed a heap of tissues, blood vessels, bones, and so on, would my opinion vanish? Where in that bloody mess am I to find the consciousness that would vindicate my opinion? But the tissues and nerves are irrelevant to the question of consciousness as are the circuit boards and transistors.

Aleksander's first error is to think that the seemingly unbridgeable gap is between bits of physical stuff (whatever they might turn out to be) and what we call thoughts, emotions and consciousness. He thinks that physics (or neurophysiology) and the philosophy of mind are at root talking about the same thing, only in different terms, and therefore it is a matter "of arriving at consensus among academics". But the problem is not simply a matter of semantics or linguistic analysis, nor, therefore, a matter of consensus. It is a matter of ontology and substantive truths. Knowing the physical (neural, or whatever) side of a creature does not entail knowing its corresponding subjective mental side.

His second error is to take conscious experiences as items to be studied independently of the first person point of view, again mistakenly thinking that the gap is between neurons (or whatever) and qualia (eg, the sensation of redness of a red nose). Conscious experiences are constitutively bound up with a particular point of view. What this means is that it is not, as it turns out, that a particular point of view happens to be attached to conscious experiences.

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Rather, it is part of what it is to be a conscious experience that it is essentially subject to a particular point of view. It is an a posteriori truth that if something is a pearl it dissolves in wine; but it is an a priori truth (and not "an act of belief" as Aleksander thinks), that if there is conscious experience there must be a point of view. Conscious experience can occur only when there is a point of view.

This leads to Aleksander's fallacious claim that he can "know directly what it is like to be a Magnus". It is precisely this that Aleksander cannot do. From his third person perspective he cannot possibly know, let alone know directly, what it is to be Magnus. To know that, he has to become Magnus. It is difficult to understand what would be left of what it is like to be Magnus if Magnus's first person point of view were removed, or adopted by another. Aleksander can interpret Magnus's behaviour, as he says, as being aware, emotional, and so on, and then go on to propose postulates and corollaries. But so what? Knowing what it is like to be Magnus, or any particular organism, is not a matter of expertise.

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In the case of objects in the world, like water, gold, planets, and so on, that exist independently of us, there is a clear separation between the object and the way the object is presented to an experiencing subject. However, in the case of an experience itself, such independence and separation are impossible. This does not entail that our understanding of our human subjective facts is logically impossible; as Frege said, mental terms that refer to such facts often bear an objective sense. The suggestion that the problem of the metaphysical irreducibility of consciousness is open to Aleksander's, or to any other, scientific attempt to "lay (it) to rest once and for all" is that result of a deep misunderstanding of that problem. But it would seem that what Aleksander means when he pleads for a consensus is that we should all simply accept his version of the story. That is not how philosophy works, and I rather thought that it was not how the sciences worked either.

ANDREA CHRISTOFIDOU Worcester College, Oxford.