If a computer appears to possess intelligence, then we need to consider why it appears so. One reason might be that it is intelligent. Another might be that has been constructed to appear intelligent and is a good fake. There are in fact a lot of programs that seem to be like that: good fakes - in particular, ELIZA, designed by Joseph Weizenbaum in the 1960s, and others inspired by it. These are basically tin-pot little boxes of tricks that are very effective at giving answers that appear to be intelligent.

Lesser animals have brains that resemble ours in some ways, but not others. We don't yet know which aspects of our neurology give us self awareness. So we are not in a position to tell whether lesser animals are self-aware by comparing their brains to ours.

Do you think that it is programming or neurology that gives rise to self-awareness? If it's the former, then do you think that a very very very simple program would give rise to self awareness? If its the latter, then do you think your toaster has neurones?

I'd suggest that an animal with a very simple brain isn't self aware, and the same goes for a computer with a very simple program.

What you seem to mean by "the mysterian attitude" is captured by your later phrases, "throwing in the towel" and "helplessness". In this sense, I don't know that there are any philosophers who count as mysterians, though I suppose Colin McGinn, who holds the view that our mind just cannot entertain the concepts necessary to solve the mind-body problem comes closest. He calls his view "cognitive closure". The idea is that human minds, like those of other animals, have an innate restriction on the range of concepts available to them. But one needn't go as far as McGinn's idea of cognitive closure to acknowledge that the concepts available for framing theoretical hypotheses concerning conscious mental activity - whether based in neuroscience or computational psychology - don't seem adequate to capture the character of conscious experience. But rather than throw up our hands out of frustration, most philosophers, whether they agree with this assessment or not, are continually trying to articulate ever more precisely just where the problem lies, and only in this way can a solution be achieved. In the end there is no generally agreed criterion for when a problem is hopeless. So long as someone is willing to work on it, it isn't.

Let's call the being that results from all this replacement Sarah2. We can ask a pair of questions that seem different. One is whether Sarah2's conscious states will be like Sarah's. I agree with Mark that the answer to that question is yes; at least, it's hard to see why it would be no. But we can ask another question that seems to a different one: is Sarah2 the same person as Sarah? That's a lot more controversial.

A comparison, based on an example by Peter van Inwagen: Suppose little Johnny builds a house from a small number of blocks and leaves it in the middle of the floor. And suppose that I come in and clumsily kick the house over. If I re-arrange the blocks in exactly the same way, then the house I assemble will be indistinguishable from the one Johnny built, but it's not so clear that it's literally the same house. And if I actually replace the blocks with new ones that are just like the old ones, then it's even less clear.

So if we cryo-freeze Sarah, interrupting her normal biological and psychological processes, and then perform this massive replacement, there's at least room to wonder whether it's literally the same person. Sarah2 will no doubt think she's Sarah, but she could be wrong for all that.

This is part of a big debate, of course. One good collection that provides a wide range of background readings with a nice historical introduction is Raymond Martin and John Barresi's anthology Personal Identity, published by Blackwell.

Let’s start with a different case. When you see a mountain, you see an object miles away, even though the visual experience is in your brain. The mountain doesn’t have to go into your brain (thank goodness) in order for you to see it, because the brain can represent the external object. The case of the pain in your hand is not exactly the same, but here too it seems that one thing (in your head) is representing another thing (in your hand).

Perhaps it is stranger to suppose that we represent something outside our head as having pain that that we represent something outside our head as having the shape of a mountain, but something like that seems to be what is going on. And this may seem less strange in light of the fact that we know anyway that we have the power to represent things that aren’t actually there, for example in a case of hallucination. So the fact that the pain isn’t actually in our hand does not mean we can’t perceive it as being in our hand. I don’t want to sound complacent.

The source of the ability of the mind to form representations of things as being outside the mind is one of the great mysteries of philosophy. But granted that we have that ability, the fact that we perceive some pains as being in particular parts of our bodies may not pose a huge additional mystery.

You could have had lots of conscious experiences yesterday that you forget today. What makes an experience conscious is its character at the time, not the traces it leaves in memory.

This raises the tantalising question of how you know that you haven’t had all kinds of wild experiences in the past that that you have forgotten. This is an interesting inversion of more familiar sceptical arguments, which tend to assume that we do know about our experiences but question how we can know what caused them. It seems clear that I do have reason to believe that I have had some experiences I now forget. After all, I have reason to believe that my memory is very imperfect. For example, I have reason to believe that I had many more experiences as a child than I can now recall. At the same time, there are lots of crazy possible experiences that I have reason to believe I never had. In many cases, the fact that I don’t remember having an experience makes it pretty likely that I didn’t have it.

There are a number of good articles on consciousness in the Stanford Encyclopedia of Philosophy (to which there is a link at the right of this page).

"Higher" and "lower" can be quite slippery terms, and your not likely to find philosophers using them in serious contexts. But one might say that different forms of consciousness can be distinguished by the different capacities they possess and the relative detail, discrimination, or complexity of those capacities. So, a form of consciousness that were capable of 600 shades of emotion might be described as more complex than one with only 2. A form of consiousness that possessed self-consciousness, a distinction between self and world, a capacity for memory, for imagination, for planning, for deception, for long attention spans, for causal reasoning, for symbolic thought, for invention, for metaphor, for memory, for mathematical reasonsing, for logical reasoning, for abstraction, for language acquisition, for a vocabulary of the size of the English language, for spatial conceptualization, for music, etc. might be thought of as "higher" than forms of consciousness without any of these capacities.

Now measurement, that's something else again. I suppose I'd say that each of these (and many other) capacities may be subject to its own form of measurement. It's the business of psychology to do that, in large measure.

Hi Martin. I'm not sure about your justification for not studying philosophy (the intention of which is to encourage thinking things through for yourself!), but you'll be glad to know that there are plenty of philosophers who think along similar lines to those that you mention. There are too many to list, but two prominent philosophers concerned about the kind of big picture that you mention are Daniel Dennett (Consciousness Explained, Darwin's Dangerous Idea) and Fred Dretske (Naturalising the Mind).

If one thinks of 'atoms' as ultimate constituents of matter, indistinguishable apart from their spatial and temporal position, then it is hard to see how changing them for identical duplicates at the same location could make a difference. (I'm interpreting the experiment as replacing every atom with an identical duplicate: same atomic weight, same charge, etc.) After the experiment, one would have replaced every atom with a partner with exactly same causal powers at the same location, and it is hard to see how this could effect an overall difference in her consciousness. The only difference between Sarah before and after the operation is an historical one: the atoms in Sarah after the operation would have a different history to those in Sarah before the operation. But it is difficult to see how this difference could make a difference to Sarah's consciousness. (Going through a freezing process might make a difference to her consciousness though!)

It is clear that pain is not the only bad thing (harm) that can happen to people. For one thing, they can be killed. They can also be disabled or deprived of freedom or pleasure. Being deprived of pleasure is not the same as being caused pain. Obviously, one can be killed in one's sleep and so never know it happened or even that it was going to happen. Generally people know when they are disabled, but people can lose a leg without knowing it right away, if they have been in an accident. If it is a mental disability, that can happen to someone without his knowing, and it may be that he never knows. People can also be deprived of freedom or pleasure with knowing, although usually they will find out about it. With regard to suffering pain, it seems as if people can be in pain without being conscious of it, at least for some period of time.

If you mean by "to suffer," to "suffer a harm" and not merely to "suffer pain," then it is clearly possible to suffer without knowing it. And even if you mean by "to suffer" "to suffer pain or other unpleasant feelings," it seems that one can suffer for at least some period of time without being conscious of it.

I think that it is common to associate one's sense of oneself with a specific bodily location. I recall thinking (when I was a young child) that my thoughts were located in my throat right behind my tongue. I now believe that my thoughts are not located anywhere--not in my brain, not in a mind. There is just thinking, constituted by neural activity. The neural activity constitutes the thinking, but is not identical to it. It is an essential property of your thinking that good jobs are scarce (say) that it is about jobs. But it is difficult to see how being about jobs could be located in a definite place in your brain. Self-awareness, too, is a matter of thinking. Your being aware that you are thinking that you will probably get a good job is an instance of self-awarness. It is no more located anywhere than is your thinking that good jobs are scarce.

You can be a materialist and still doubt that all phenomena are localizable. Suppose that you play poker on the internet; where is the game? Nowhere, I think.

In short, someone blind from birth may or may not subjectively feel centred in some other part of her body instead of behind her eyes. But I am doubtful that knowing this would give insight into the nature of self-awareness.