My little toe is conscious, and it is a part of me, perhaps even a "constituent" part. I put in the scare quotes because I am wondering whether "constituent" means "essential"; if it does my big toe is not a constituent part of me. But if "A is a constituent of B" means "A is part of B", then my big toe is a constituent part of me, but the phrase "constituent part" is a tautology - it says that same thing twice. Are there parts of me which are not constituent parts, but some other kind?

You can imagine after surgery a doctor asking, "Is your little toe conscious?", and the answer might be "Yes", and working through to the big toe; the answer then might be, "No".

It is not at all obvious why we should feel the Cartesian tug to say that it is I, not my big toe, that is conscious, except for dubious epistemological reasons such as that we can imagine the consciousness without the toe. The same seems to be true of my psychological parts in Descartes' sense in the Meditations. My thinking might be highly conscious, my feelings almost or completely unconscious, perhaps to my detriment, or the other way round. Is there any reason beyond a fondness for the unity of panpsychism (everything is more or less conscious) to suppose that individual cells might be? You might suppose that my armchair is conscious, but there is no special reason to think so, whereas there is for my cat. Cells don't seem to have the psychological activity usually associated with consciousness.

Naturally my little toe is not a person (or a "self") but why should that prevent it from being conscious? Wasn't that Descartes' mistake?

It's possible that the constituents of a conscious being might be conscious, though there's no strong reason to think that it's true. Some philosophers have speculated that there are primitive little events or occasions of experience that, when arranged properly, make up minds like ours, though this isn't a popular view. Perhaps a little less odd is the possibility that each hemisphere of your brain contains a separate stream of consciousness. The philosopher Derek Parfit (among others) has had some interesting things to say about this based on evidence from cases of people whose corpus callosum (the bundle of nerves connecting the two hemispheres of the brain) has been cut. Whether this would be a case of one conscious being with parts that are also conscious is harder to say.

In any case, from the fact that you are conscious, nothing follows one way or the other about whether your cells are. To infer that they must be would be to commit the fallacy of division. To infer that they must not be would also be a fallacy, though one without a name. It would be a bit like inferring from the fact that the Supreme Court has a lot of power that none of its members do.

Why should the possession of intelligence (whatever we mean by this, but say it means winning chess games against the world chess champion, winning bridge games with bad partners against the world bridge champions, issuing correct diagnoses for car repairs, predicting stock market fluctuations, analyzing individual psychology, and so on) require consciousness? We know that when Kasparov played Deep Blue he "sensed" a "weird" and "alien" kind of consciousness - or said and thought he did. I have the same thing with my very complicated telephone handset - it is against me, spitefully, deliberately and consciously. If we allow that playing chess well involves intelligence, then Deep Blue or Deep Fritz or Shredder show the following thing: intelligence does not require consciousness. If we deny consciousness to the systems, then your question does not arise at all, because (a) is false. (I have used "consciousness", but "self-awareness" implies much more, including I think the critique of elements of behaviour.)

It is true that a number of psychologists treat intelligent use of mirrors as evidence of self awareness. But I am not convinced. Animals can gather information about their own bodies via various forms of perception, including, of course, vision. Some can also use a mirror - extending the range of their vision - to get information about their own bodies. But I don't see how that implies that they have any concept of self. My guess is that lots of animals do have something that we might reasonably call 'self awareness'. But I don't know of any serious evidence for this.

I am an animal, and I am at least intermittently self-aware, so yes.

But I'm guessing you wanted to know whether non-human animals are self-aware. We could spend some time trying to sort out exactly what counts as self-awareness, and that would be a lengthy though worthwhile exercise. But the short and plausible answer is that some are and some (perhaps most) aren't. One reason to think that some are comes from research with mirrors. Some elephants and some chimps, at least, seem to be able to figure out that what they're seeing in a mirror is their own reflection. You can read a short account of some of the research here.

I think that an organism must be conscious in order for there to be something that it is like to be that organism. This may seem like an obvious truth, but some people believe that there is something it is like to be asleep even though we are not conscious when sleeping, and some people believe that there is something it is like to have unconscious desires. If you believe either of these things, then you may well believe that there is something it is like to be an animal without consciousness. But I have trouble understanding the phrase “what it is like” to be a bat without assuming (at least some sort of) consciousness on the bat’s part.

To decide whether a particular animal is conscious at a particular time, I would want to know whether it is engaged in certain sorts of information tracking. To be conscious is to be attentive in some way and being attentive, I suggest, requires one to track a given object or event across time – despite various changes in its appearance or surroundings. (A strong version of this claim would equate consciousness with information tracking. A weaker version would treat information tracking as necessary, but not sufficient, for consciousness. Either way, though, an animal’s inability to track information would indicate a lack of consciousness.) A bacterium that responds to changes in temperature without keeping track of the object that is the source of heat, or without keeping track of its own movements through space, does not pass this test.

Given the above assumptions about consciousness, and given what I know about the abilities of different animals, I would draw a dividing line between insects and fish -- concluding that there is not something that it is like to be an insect (since insects respond to stimuli without tracking objects or event) but there is something it is like to be a fish (since fish do track objects and events).

I don't think your question is strange at all. In fact, many philosophers of mind have been pre-occupied with just this very question for quite some time. Then again, perhaps that just makes us strange!

It might help to start by being clear about what exactly you mean by consciousness. Sometimes we talk of being conscious in the sense of being awake as opposed to being asleep, or as opposed to being passed out after an overindulgence of some sort. Sometimes we talk about being conscious in the sense of being aware, so we might sometimes be conscious of the ticking of the clock and sometimes not. Philosophers often talk about consciousness in a third sense to refer to the subjective aspects of our experience. To use a phrase brought into play by Thomas Nagel, there is "something it is like" to smell coffee brewing, or to see the vivid colors of a sunset, or to have a sharp pain in your toe. This is often referred to as phenomenal consciousness, and trying to find some way to account for it has become known (following David Chalmers' work in The Conscious Mind) as "the hard problem of consciousness." What makes the problem so hard is that it seems that phenomenal consciousness is not just built in to the brain, and so it's hard to know how we can account for it. It seems that we could imagine all of our neural mechanisms being exactly the same as they are and yet we might lack consciousness. Chalmers makes this point through the example of our zombie twins. Philosophical zombies aren't like the zombies of horror movies. They don't eat flesh, for example. They are supposed to be exactly like we are--molecule for molecule identical to human beings--but without any phenomenal consciousness. All is dark inside. So both zombie Amy and I might be typing at our keyboards, but whereas I am having the experience of feeling the keys touch my fingertips, and whereas I am savoring the delightful taste of the Diet Coke I just had a sip of, zombie Amy doesn't have these experiences while she types and sips. She types and sips without feeling or tasting anything at all. If zombies are conceivable, and many philosophers have thought they are, then it does indeed seem like consciousness is an "add-on" to the physical stuff we're made of. It doesn't seem intrinsic to the skill of typing, say, that one would have to have the phenomenal experience of feeling the keys on our fingerstips.

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.