Compare the case of pain to the heat of spicy curries or steamy saunas: I recognize certain green curries to be just as hot/spicy as certain red curries, but I have a higher tolerance for the heat/spicyness of green curries; and I can tolerate steamy saunas better than in dry saunas even when I experience them as equally hot. I am not less sensitive to the heat of green curries or the heat of a steamy sauna, but I am not bothered by them as much as I am bothered by the heat of spicy curries or dry saunas. Why isn't pain like this -- tolerated differently in different forms, or by different people, even when the amount or degree of pain is recognized to be the same?

You might think that pain just is intolerance, and that the degree of one's pain is equivalent to the degree of one's intolerance, so that finding a sauna less intolerable should be equated with finding it less painful. But since the two words, "pain" and "intolerance" are used in rather different ways, and since (as you note) people do often say they are more or less tolerant of pain, it would not a linguistic equivalence. Still, as you suggest, if the evidence for one is equally evidence of the other then perhaps they are in fact the very same thing.

I do not think the evidence for one is the same as the evidence for the other, however. Aside from introspective reports (which constitute one kind of evidence, after all), here are some (more objective) kinds of evidence that help to distinguish insensitivity to pain from tolerance of pain:

(1) A racing heartbeat and tensed muscles (showing sensitivity to pain) together with a calm demeanor (showing tolerance of pain).

(2) A spontaneous cry or flinch (showing sensitivity to pain) together with willingness to continue painful procedure or activity (showing tolerance of pain).

(3) An ability to give nuanced reports on the character of one's pain (showing sensitivity to pain) together with lack of interest in using pain medications (showing tolerance of pain).

While (1) and (2) may suggest two parts oneself -- one responding automatically and the other more reflectively resists these automatic responses, (3) suggests an interesting, if unusual, disconnect between the feeling of pain and the awfulness of pain. You may be interested to look at a recent book by Nikola Grahek, entitled Feeling Pain and Being in Pain, that describe some carefully documented cases of pain without painfulness and painfulness without pain.

There are lots of things that don't exist that we can conceive of, most obviously fictional characters and objects, though our conceptions of them may be less detailed or thorough-going than our conceptions of things that do exist. (They may also be more detailed. We may know more about the characters in Tolstoy's novels than about some real people.) We can conceive of an elixir of youth, though there may not be such a thing, for example. And if consciousness exists, where does it go when you are meditating or fast asleep? Well, why does it have to go anywhere? Isn't it more like a noise, say, that is real enough in its way, but which just shuts down or disappears when the thing making it go stops, and doesn't have to go anywhere? Of course if the individual consciousness is a sort of stuff, rather than a kind of attention, a substance even, in the philosophical sense, then presumably it keeps on going even if it isn't with you any more. But it is difficult to see how that would work; what happens to your consciousness if it continues to exist but you are not conscious of it? It is hard to say, as Aristotle would say! On the other hand it is easy enough to see how you can go on with or without consciousness. It happens to me every day.

The fact that one thing causes another does not mean than the second could not exist without the first. Consider the case of a forest fire, for example. A carelessly flung match could be the cause, and yet (a) the fire could continue even after the match is destroyed, and (b) other things, such as a bolt of lightning, could substitute for the match as cause of the fire. Similarly, one could think (a) that brain activity causes consciousness, but consciousness can continue even after the brain is destroyed, or (b) that things other than brain activity, e.g. cosmic vibrations, could also cause consciousness. Without evidence to support these possibilities, they remain mere possibilities; but they do show why the causal relation you cite does not "destroy an ideas of an afterlife".

If you think that an individual's consciousness is not just caused by the activity of her brain but is identical with it, then that consciousness must indeed cease when the activity of that brain ceases. But many who agree that there is an "obvious" causal relationship between consciousness and the brain do not think that consciousness is identical with the brain.

It doesn't.

There are several possibilities here. One is that there is a causal relationship between the physical brain and a non-physical mind, which can still make sense of the idea that when alcohol is coursing through your veins into your brain it causes your conscious experiences to be funky or when a part of your brain is lesioned it causes mental disorders. This view is Descartes' dualism. If it is true, then presumably your non-physical mind (or soul) can survive after your physical body dies (though it's hard to imagine how things would be for your bodiless soul in "heaven"--e.g., how do you find grandma? and what would you do for fun?). This view becomes less plausible the stronger the correlations between brain states and mental states become (the soul seems to have nothing left to do).

So, supposing such dualism is implausible and we assume this evidence of a causal relationship between brains and consciousness is evidence of a physicalist view, one that says the mind just is the brain or that mental states are constituted by brain states, etc. Then, perhaps you are asking how there could be an afterlife (i.e., how our conscious selves could survive) after our physical brains die. One answer is that, even though our minds/selves depend entirely on our brains (and perhaps bodies), we can survive after our bodies die, because God reconstitutes our bodies in heaven (or more generally, because some power reconstitutes our bodies somewhere). Perhaps this sounds implausible. But it shouldn't to religious people. In fact, the way the Bible talks about life after death sounds more like this than like an afterlife of non-physical entities floating around (can something non-physical float?). Jesus is said to have risen bodily from the grave and ascended to heaven. If one wants these heavenly bodies to be indestructible, then God would have to either give them special (spiritual?) powers to avoid normal physical decay or rejuvinate them regularly. Again, there are no obvious problems with this view of the afterlife and several advantages over the view that we can survive after death only with non-physical minds.

All of this suggests that any conflicts between physicalism (or materialism) and theism (or religiosity) need not be about life after death but are more likely to be about the existence of God (or certain properties of God or of heaven) given a physicalist or naturalist worldview. On a naturalistic view, it is hard to make sense of where or how (a non-physical) God exists or where a heaven where God reconstitutes us exists or what explanatory work is being done by God or heaven (beyond alleviating our fear of death).

Finally, if we take the functionalist view that our mental states are essentially complex functional interactions, one might think we could survive the death of our brains if the functions (or "programs") of our brains could be adequately replicated in an artificial replica (e.g., a complex computer or a Matrix or something). Whether this would count as personal survival is an interesting question. On this view, perhaps heaven is a matrix!

There is one very general reason and two more specific reasons that philosophers are interested in the question of whether consciousness is identical to a particular bodily state.

The general reason is this: we are interested in knowing what the most basic constituents of the world are, and how they are related. If consciousness is not identical to a bodily state, then we want to know what sort of thing it is and how it seems to be able to interact with the body. But if consciousness is identical to a particular pattern of brain waves, for example, then we are justified in thinking that mental states are not something different than physical states and consciousness can be understood through the study of the brain. In short, we want to clarify different categories of existence, eliminating the confusions that result from thinking that there are two (or more) things when there is just one, or thinking that that there is just one thing when there are actually two (or more).

A more specific, existential reason that we are interested in whether consciousness is identical to a bodily state concerns the possibility of life after death. If consciousness is identical to a particular bodily state, then it cannot continue after that bodily state ceases to exist. So those who think that there is life after death must reject the claim that consciousness is identical to a bodily state. (There are physical particles and forces that continue after the death of a particular body, of course, so if consciousness is identical to these particles and forces then it may continue after a particular body ceases to exist. Most identity theories, however, equate consciousness with a brain state.)

There is also a social or ethical reason for being interested in whether consciousness is identical with a physical state of the body. If there is such an identity, then anything that lacks the relevant physical state (a robot, an insect, a Martian, or a cloud of dust) also lacks consciousness, and needn't be treated as though it were conscious. On the other hand, if there is not such an identity, then there could be consciousness in many places we don't expect it to be, and an appropriate sort of humility is called for.

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.