Espie asked:

What does it mean to say that there is a contingent identity between mental states and brain states?

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This is a good question, but not an easy one to answer in a short space. I recommend you go here:
http://www.stanford.edu/~lmaguire/phil186/smart.htmto read a nice essay about this.

In addition, I'm really not clear that this whole issue isn't largely linguistic, i.e., about language use, as
Wittgenstein would probably hold. On the other hand, one might ask whether there's any point in the
label "contingent identity" and whether it does not oversimplify a complex issue. But, anyway.

So, I'll start by claiming, first, that contingency means, basically, that something depends on some
kind of knowledge, and so, for one thing, it isn't certain; that for example if taking a taxi is contingent,
there are things you have to do to take a taxi, like pay, open the door, things like that, right? Whereas
taking a taxi isn't contingent on what kind of shoes you're wearing, usually (let's say). What about
"contingent identity"? Well one way you could think of it is in terms of uncertainty: you could say that if
we're uncertain about what something is, then its identity to something else is contingent... on our
finding out, for example. We could say that light is contingently identical to electromagnetic radiation
before we took physics, or something like that. The classic example here is the planet Venus and the
morning star; they are the same, if you know a bit of astronomy. Is this more than a linguistic issue, at
base? I'm not going to go further on that question.

But there is another sense of "contingent identity" which is deeper, perhaps. Suppose we're talking
about the way we understand something, and that in order to understand something in a particular
way, we have to have more than just knowledge about it, we have to have a particular mental
perspective. Now, that perspective might be a direct result of knowledge as in the above, or it might
be a result of a worldview: the difference between, say, a wise person and a person who knows a lot.
Or it might be the difference between what might be termed "internal" perspective: that we experience
brain-states as feelings, but we see them as traces on oscilloscopes, for example. Is there really a
difference here, between knowledge and what I'm calling "perspective"? Well, you know, I really don't
know. The debate is still raging, out there in the world of philosophy, such as it is.

So if we assume that a) there are entities we can term "mental states", and b) other entities that we
can term "brain states", we've already divided things in a particular way, haven't we. Oh, well. Now,
we notice that there seems to be a correspondence between brain states, e.g., neural firing, or
transmitter levels, or fMRI readings, or suchlike, and mental states, e.g., the smell of hamburgers,
fear, the thought of no thought of tomorrow, and so forth. So what does that correspondence mean?
Well, it could mean that mental states are in some way exactly identical to brain states, i.e., if and
only if ("iff") we are manifesting brain state B(A) then we are in mental state M(A). And if you say "iff"
then the converse works too, and we can say, "iff we are in mental state M(A) we are manifesting
brain state B(A). Well, there's nothing contingent about that, is there. So we can't use "iff" if we're
talking about contingent identity; we have to say, "if we are manifesting brain state B(A) then we are
in mental state M(A)". That's a very different thing, because now we can't say, "if we are in mental
state M(A), then we are manifesting brain state B(A)", and we've opened the door to a nasty dualism.
You see? If that last kind of statement (with "if" instead of "iff") is true, then maybe it's true that we can
be in a mental state but not in a brain state. So, although we have to feel something, let us say, if
someone pokes at our brains... nonetheless maybe we can die and our brains can rot and we can still
feel things, if the contingent statement above is really the case. In other words, it doesn't make
anything true, but it allows for the possibility.

Well naturally then there are a lot of materialists, including me, who don't like this possibility... and
either want to devise arguments supporting the "iff" kind of situation, or just want to say that the whole
thing is silly to talk about now, since we just don't have enough real, hard, data to make a decision
one way or another. That's my take on it, anyway. But, the arguments go on... you might also look up
the whole controversy about Mary and the black-and-white room. This is a very nasty and complex
area in philosophy of mind, not one to be approached casually.

Steven Ravett Brown