Paul
I need to explain to you exactly
how you physicalism ends up with no referent for "subjective experience". This is not the primary problem - it is the symptom of another problem. Just as "subjective experiences" has no referent, you also have another term which has
two different referents. This other term is "physical" and it is the definition of "physical" which has caused the problem. Why?
These two terms
normally (when we aren't having this debate) have the following referents:
Subjective experience -----> The sum total of all your conscious experiences, everything that's ever appear in your mind.
Physical brain processes -----> A computation in grey matter in your head.
In this standard terminology "physical" is clearly refering to what we called P1 before. If you are sitting in front of a mirror with a hole in your forehead then "physical brain process" would be something you could see in the mirror. When you say "physical" you are using this as one of your referents - you are refering to the whole physical world as you experience it, from your own hands to the most distant star you can see. This is
referent 1 for "physical".
But physicalism doesn't stop there. Even though you already agreed that experiences of a physical universe shouldn't be confused with the external causes of those experiences, you (and physicalism) also declare that P2 (the mind-external reality which causes those experiences)
is also physical. When you are sitting in front of the mirror, you see a physical-1 brain (in the mirror), but the physical-1 brain isn't the proximal cause of your subjective experiences. By contrast, the physical-2 brain isn't in the mirror, but
is the proximal cause your subjective experiences. So they aren't the same thing. Your physical-1 brain is not a synonym for your physical-2 brain. So you now have a
referent 2 for "physical".
So you now have two terminological problems, not one:
You have one word ("physical") which has two referents (physical-1 and physical-2), and there is much potential for confusion if you subsequently conflate them without noticing you've done it. Therefore you need a new term for one (or both) of these referents to avoid the risk of serious confusion.
You also have another word/term ("subjective experiences") which has no referent at all, even though you really want it to have one.
So I am hoping you can see what has gone wrong here. The fact that "subjective experiences" has no referent is a symptom of the double definition of "physical". It is a symptom of the mistake of confusing P1 and P2 by calling both of them physical. Why did you want to call them both physical? It wasn't because that was a sensible term to use - it was because you were trying to defend physicalism by assuming it was true ("begging the question") in the the following way:
If physicalism is true then everything must be physical so P1 is physical and P2 is also physical, even though they are different. They are just "different sorts of physical".
So you have ended up with two different referents for the single word "physical" and no referent at all for "subjective experience". At this point, somebody like me comes along and tries to claim your definitions are all messed up. But when I try to fix them you will say "but you are using all that dualistic-influenced talk to define your terms" or falsely accuse me of "begging the question." All I am actually trying to do is get to a point where each term has one referent and nobody is confused about meanings. But every time I try to do that I get falsely accused of being a dualist and the existing physicalist terminological mess is defended to the hilt instead of being corrected. Because I am aware of exactly what has gone wrong with the terminology and you aren't aware of it at all (and wouldn't permit me to correct it - until now), I can play logical games with you. As soon as you give me a definition of "subjective experience", I can use your definitional confusion to construct a logical proof that your definitions are incoherent. But I do not want to play logical games with you as if I was a stage magician pulling proofs against materialism out of a top hat. I'm trying to explain to you how the trick works. No actual magic is involved.
Geoff
edit NB: If you followed all that then it should now be clear how the term "qualia" got invented. If you define physical as P2 then you've got this extra referent (the brain in the mirror - what a physical brain actually looks like to you). The person who wishes to define qualia is doing no more than inventing a new term for one of your usages of "physical" - and it is a term that is now definately needed if we are to distinguish P1 from P2. If you want to prohibit them from doing this then you are still left with a referent which has no term, forcing me to invent yet another new term to add to the collection of supposedly referentless terms you can't define : Mind, mental, subjective, 1st-person, qualia, experiences, P1, ....
You've got a referentless term ("subjective experiences") and you've got a termless referent (the thing qualia refers to). But even though the referentless term quite obviously refers to the termless referent (qualia really are subjective experiences) the physicalists refuse to allow the definition of this term! 
