Had a long debate two nights ago about the unobservability of subjective experience. For simplicity's sake, call it consciousness. My argument is that one can only gain objective knowledge of an observable object, indeed, its observability is what makes it an object. Now, I can observe a rainbow. I can observe the Sun rising and setting. I can observe a human. I can observe the human reacting to a stimulus. I could in principle observe a signal traveling through the human's nervous system, reaching the brain, setting off a storm of activity, I can observe the chain of cause and effect and (in principle) understand how it results in a signal being sent out again, and how that signal results in the exclamation "Ow!", and how another signal is sent out, and how that signal results in the hand being retracted from the hot surface. I can continue observing and (again, in principle) understand why this results, five days later, in a complicated series of signals and how they result in the telling of a story about the stimulus that occurred five days ago.
I cannot observe, in any of this, the fact that there is a consciousness there that experiences--as its subject--the stimulus, and that experiences--as its subject--the reaction to the stimulus.
The existence of consciousness will never, ever be explained physicalistically. For this to happen, there would have to exist an observed phenomenon that logically forces the positing of consciousness. Don't these people realize, that their own doctrine insists that all physical phenomena can be explained physically, i.e. in terms of other physical phenomena? So then imagine you have a human in front of you; in the laboratory, under dissection, or otherwise being studied and observed. This human is a physical object. What can you hope to find in your observation, but more physical objects? Imagine you have spent a lifetime observing the brain. Imagine you are approaching a perfectly complete knowledge of all the physical processes therein. When do you suppose you will come across something that will force you to say, "Ah-hah! This could only be caused by consciousness." Doesn't that seem to be most un-scientific-- doesn't it seem that whatever you find there is just going to be like anything else in the physical universe, an object with an objective cause...
Arrrgggg! What really frustrates me is that all of this ranting is totally unnecessary. All that is necessary is the following: Solipsism is always possible and logically consistent with every possible set of objective statements (to see this, consider how you would convince a solipsist that he is wrong).
So:
A) No amount of material observation will convince me that subjectivity (a consciousness, if you will) exists.
B) Nevertheless I am intellectually certain that at least one subject exists, and by the way, morally certain that many subjects exist.
Therefore, to allow subjectivity to be theoretically intelligible I must posit the category of the immaterial.
Okay, so this doesn't prove that physicalism is false, just that it is unintelligible. I.e., although it might still be asserted that all things are material (including consciousness), this does prove that it is impossible for us to ever understand all things as material. So if you are a fan of intelligibility, you should start considering the immaterial world. If on the other hand you prefer the unintelligible to the mysterious, well, go ahead and subscribe to physicalism.
Next up: Moving from the immaterial consciousness to the immaterial soul. And maybe a bit more about unintelligibility and mysteriousness, two categories I have been thinking a lot about recently.
