Experience is a self-evidencing fact. It is on the evidence of experience that I say "I experience", "There is experience", "Experience exists" and so on. So, I take the existence of experience as the first premise, the common ground from which scientists and philosophers of consciousness proceed to describe and explain the brain/experience relation.
[1] Experience exists.
To show that the brain/experience relation is not the relation of logical identity, I will borrow the example that Daniel C. Dennett uses for this purpose.
In his video presentation to the 5th Online Conference on Consciousness, Dennett guides the viewers through the process of inducing an afterimage of an American flag. Then he focuses the viewer's attention on one particular red stripe and draws a conclusion based on Leibniz's Law of Identity (the Indiscernibility of Identicals).
If A is a red stripe and nothing in the brain is a red stripe, then nothing in the brain is identical to A" [Dennett. 2013. @time 12:10]
A non-identity claim such as this is an important premise in an argument for dualism from experience; and, I adopt the following version as a premise.
[2] Nothing in my brain is identical to the red stripe in my experience while I am experiencing a flag afterimage.
Immediately after stating the non-identity claim, Dennett admits that dualism follows unless the materialist has an reply, a defense sufficient to ward off the possibility of dualism. Dennett then shifts to advocating a particular defensive move. He argues that the defender of materialism must deny the existence of the red stripe in experience.
We can talk about 'that red stripe'. ... We have no trouble referring to that red stripe. ... It's a thing for us, as good as any other thing in our experienced world. It's a part of our experience in that sense. And yet I'm saying it doesn't exist. It doesn't exist. It only seems to us that it exists. [Dennett. 2013. @ time 20:45]
Thus, the strategy of the Dennett Defense to the Argument for Dualism from Experience consists of affirming something like
[3-Dennett] The red stripe in my experience while I am experiencing a flag afterimage does not exist in any sense whatsoever.
I deny [3-Dennett] by adopting a conflicting premise based on Searle's insight that first-person phenomena exists while being experienced.
[3] The red stripe in my experience while I am experiencing a flag afterimage exists while I am experiencing it.
Proposition [3] is introduced as a premise; but, given certain reasonable grammatical conventions, [3] follows from [1].
[1] is stated in a depersonalized way appropriate for stating a general philosophical principle. However, it is on the evidence of my experience that I assert [1]; so, based on the same evidence, I might also say
[1.1] My experience exists
Could it be the case that experience exists but that my experience does not exist? I would say 'No!'.
[1.1] uses the collective singular form of 'experience' which is appropriate for designating the seamless whole of experience or what Searle (1999, 2013) terms the "unified conscious field".
Furthermore, qualitative subjectivity always comes to us as part of a unified conscious field. At any moment you do not just experience the sound of the music and the taste of the beer, but you have both as part of a single, unified conscious field, a subjective awareness of the total conscious experience. So the feature we are trying to explain is qualitative, unified subjectivity. [Searle, 2013]
Suppose I induce a flag afterimage. I see the flag. I see the white wall against which I see the afterimage. I see any number of other things in my field of vision. I hear my dog barking in the background. I smell the pine scent of an air freshener. etc. All of this and more is my experience. However, to discuss its philosophical implications, I must single out some part or aspect of my experience for further commentary; and, thus, we get to the question on which the argument turns:
Can it be that experience exists and that my experience exists but that none of the aspects of my experience exist?
I don't see how. It would be like seeing a lake, noting that it was full of water, dipping a pail into the lake and pulling up a pail full of non-existent water. It simply makes no sense at all, as far as I can tell; hence,
[1.2] An aspect of my experience exists while I am experiencing it.
Now, for the general term, "an aspect of my experience", I substitute the specific aspect of my experience with which I am presently concerned. This yields the third premise.
[3] The red stripe in my experience while I am experiencing a flag afterimage exists while I am experiencing it.
There are several flaws in the Dennett Defense. I will focus on three, each of which is serious if not fatal to Dennett's case.
If Dennett does not deny [3], his recommended defensive tactic is defeated; and, he will have to find some other means to defend materialism from arguments that proceed from this point to any dualistic perspective or any other perspective (such as non-reductive materialist) he finds unpalatable.
However, as shown above, given certain grammatical conventions, [3] follows from [1]. Consequently, if Dennett denies [3], he denies [1], the existence of experience --- the philosophical analogue of a Pyrrhic victory, in my view.
One of Dennett's arguments for denying the existence of the red stripe in one's experience while one is experiencing a flag afterimage is that "The red stripe is an intentional object which doesn't have to exist" (Dennett, 2013. @17:10).
Now, I will happily grant and I suspect that Dennett's dualistic opponents and perhaps even some non-reductive physicalists would also happily grant that an intentional object does not necessarily exist as a material object; and, that the red stripe in one's experience while one is experiencing a flag afterimage is an intentional object of just that sort, one that does not exist as a material object.
However, admitting that the red stripe in one's experience while one is experiencing a flag afterimage does not exist as a material object is not itself a defense for materialists. To make the Dennett defense work, Dennett must also show one of two things:
Unless Dennett can do that, there is a defense gap.
The first option, the Searlean Option, seems especially dubious; raising two difficult two questions.
The second option, the Nihilistic Option has problems of its own with the same two questions.
The wording of Dennett's premise, that the red stripe is an intentional object which doesn't have to exist, seems to suggest that he is making a modal claim; perhaps, something like "The red stripe is an intentional object which doesn't necessarily exist". If that is his claim, he doesn't explain how to make the leap from "doesn't necessarily exist" to "actually doesn't exist" which is what he would need to show to take the Nihilistic Option of the Dennett Defense of materialism.
Assuming arguendo that Dennett somehow justifies the assertion that the red stripe in his experience while he is experiencing a flag afterimage actually doesn't exist, as an argument in favor of [3-Dennett], this tactic fails due to an obvious self-contradiction.
Dennett admits that I can refer to the red stripe in my experience while experiencing a flag afterimage; so, I'll refer to it as 'a'.
[D-1] a = the red stripe in my experience while I am experiencing a flag afterimage
Dennett admits that a is an intentional object; so, letting 'O' represent the predicate 'is an intentional object', we get
[D-2] Oa
At this point the rule of Existential Generalization (aka Existential Introduction, http://en.wikipedia.org/wiki/Existential_generalization) allows us to introduce an existentially quantified proposition on the basis of Oa.
[D-3] (∃x)(Ox)
By definition, existentially quantified propositions make existence claims. Consequently, Dennett contradicts himself by saying that a, the red stripe in my experience while I am experiencing a flag afterimage, does not exist. It's not clear how Dennett can avoid this problem; but, until he does, [3-Dennett] is an unsupported claim.
Assuming arguendo that Dennett repairs the logical flaws pointed out in the previous section, the strategy of denying the existence of the red stripe in experience while experiencing a flag afterimage has a major problem when implemented by the tactic of admitting that the red stripe in experience: if effective at all, it is simply too effective. If one may successfully deny the existence of a particular aspect of experience such as the red stripe in one's experience simply by recognizing it as an intentional object, one could just as successfully deny the existence of any and all other aspects of experience, resulting in the complete denial of experience noted by Searle.
The problem of consciousness is identical to the problem of qualia because conscious states are qualitative states right down to the ground. Take away the qualia and there is nothing there. ... Conscious states by definition are inner, qualitative, subjective states of awareness or sentience. [Searle. Consciousness and Language. p. 26]
The denial of experience may seem like an unpalatable consequence of the Nihilistic Option; but, given a choice between zombie materialism and some sort of dualism, it is not at all clear that everyone would make the same choice.
In this I am following Searle's notion of reduction.
The basic intuition that underlies the concept of reductionism seem to be the idea that certain things might be shown to be nothing but certain other sorts of things. Reductionism, then, leads to a peculiar form of the identity relation that we might as well call the 'nothing-but' relation: in general, A's can be reduced to B's, if A's are nothing but B's. [Searle. 1992. p. 112]
How can one ontologically reduce an X to some Y to which X is not identical? We can't; so, clearly, [2] indicates the failure of the identity relation on which an ontological reduction depends.
A moment's reflection should tell us that there are innumerable pairs of statements analogous to [2] and [3]; for example,
[2.1] Nothing in my brain is identical to the red stripe in my experience while I am looking at a physically instantiated American flag.
[3.1] The red stripe in my experience while I am looking at a physically instantiated American flag exists while I am experiencing it.
The Argument for Dualism from Experience would proceed just as easily from [2.1] and [3.1] as from [2] and [3]; in each case, we could draw the specific conclusion that the phenomenon in question is not ontologically reducible to brain activity. Consequently, we may generalize:
[4] Experience is not ontologically reducible to brain activity.
If experience or some aspect of experience is not identical to a material object; then, the brain/experience relation is a relation between two distinct terms each of which exists. The brain exists; and, aspects of experience exist; but, they exist in different ways. If that is not dualism, I don't know what is.
This is clearly a judgment call that I've made; meaning, a claim that this is an instance of that. Consequently, I will introduce it as a new premise:
[5] Ontological irreducibility is sufficient for dualism.
No specific type or flavor of dualism can be deduced as any such conclusion would depend on what further assumptions are introduced by advocates of particular positions. So, I will stop here.
Dennett, Daniel C. (2013). "On a Phenomenal Confusion About Access and Consciousness". http://consciousnessonline.com/2013/02/15/on-a-phenomenal-confusion-about-access-and-consciousness/
Searle, John R. (1992). The Rediscovery of the Mind. Cambridge, MA: MIT Press.
Searle, John R. 1998. "How to Study Consciousness Scientifically". (in 2002. Consciousness and Language. http://books.google.com/books?id=bvxhV-1Duz8C
Searle, John R. (1999). "Consciousness". Unpublished manuscript. http://socrates.berkeley.edu/~jsearle/Consciousness1.rtf
Searle, John R. (2002). "Why I Am Not a Property Dualist". Journal of Consciousness Studies. 9(12):57-64.
Searle, John R. (2013). Can Information Theory Explain Consciousness? New York Review of Books. 2013-01-10. http://www.nybooks.com/articles/archives/2013/jan/10/can-information-theory-explain-consciousness/