Thursday 3/22
Consciousness III: The Modal Gap
Assignments
Readings
Texts
Notes
Lecture Quiz Questions
Note that the questions below refer to our readings and discussion from Tuesday, 3/20.
- What is the Case of Fred, and what does it show?
- How does the Case of Fred compare to Nagel's bat?
- What is the Case of Mary, and what does it show?
Synopsis
It bears noting that one of the more striking features of the problem of phenomenal consciousness is that it emerges from radically and surprisingly distinct directions. In Jackson's Mary (and Fred!) we see how purely epistemic considerations can motivate a judgment against physicalism.
Today we considered a fascinating alternative to the Knowledge Argument which appears to show that purely linguistic considerations drive us to the very same direction.
Recall the failings of the Naive View and the Fregean View of linguistic communication in light of the Twin Earth Thought Experiment we recently discussed. Apart from noting the demise the Naive and Fregean views, we said little about more recent work in the philosophy of language. We began today by considering just how many philosophers have come to think about language in light of the Twin Earth Thought Experiment.
Hilary Putnam, Saul Kripke, David Kaplan, Robert Stalnaker, David Lewis, and others have proposed variations on what may generally be called the Theory of Direct Reference. Recall that the Naive View asserts that extension is determined by intension, where intensions are meanings or ideas about the term's reference (extension) in the mind of the language-user. Recall also that the Fregean, responding to the problem the Naive View has of depending on the speakers being able to compare ideas--mental states, in effect--to secure communication, posits an external realm of senses we somehow grasp in communicating. Since we grasp the same senses using the same words, communication is made possible provided we can understand how we grasp senses.
Both the Naive View and the Fregean View are called mediated theories of reference. Since grasping must involve some psychological state or other, the Twin Earth Thought Experiment counters either brand of mediated reference. The problem that "meanings ain't in the head!", as Putnam memorably put it, encourages us to stop clinging to the assumption that the reference of a term is mediated by ideas, senses, or anything whatsoever.
How, though, is linguistic communication possible under direct reference? There are different ways to explain how it goes. The version we examined in class proposes that there is an initial baptism or christening whereby a term is first used to refer. Thus the day the Titanic was christened, some famous person I don't presently care to look-up smashed a champagne bottle on the ship and declared (something like)
I dub thee "Titanic"!
Of course the Titanic was known by "Titanic" prior to this particular event, but it suffices that there was some particular event, even if not this one, at which the ship was dubbed "Titanic". This is a sort of baptism by which a term comes to have the reference it does. The use of the term from one person to the next then creates a causal history that directly ties term to reference purely in virtue of its sociolinguistic context. Putnam calls this process the "division of linguistic labor". The idea is that it is by no means up to us what our words mean. Far from it. What they mean depends on what the community of language users takes them to mean, which is given by their causal history in the community.
Without evaluating the claims made on behalf of direct reference, we noted that Kripke uses special terminology to talk about terms which directly refer: He calls them "rigid designators". The rigidity he has in mind is quite strong. As Kripke understands them, rigid designators have the same reference at every possible world (at which, we might add, the reference exists.)
This may seem counter-intuitive. After all, why couldn't "Titanic" refer to some other ship at another possible world? Couldn't the language users at another possible world have used "Titanic" to refer to, say, a dinghy on the Queen Mary, just as my doppelganger on Twin Earth refers to a different substance by "water" than I do?
Presumably they could, but we are only interested in the terms as we use them. That is, our linguistic practice fixes the referents of rigid designators, so "water" refers to H2O at every possible world as it is used by us.
Another counter-intuitive implication of direct reference is the Principle of the Necessity of Identity. That is,
If X = Y, then necessarily X = Y.
In terms of possible worlds semantics,
If X = Y at the actual world, then X = Y at every possible world.
I concluded today by trying to explain why this should strike you as counter-intuitive on first encounter.
Consider that
Mark Twain = Samuel Clemens at the actual world.
That is, Samuel Clemens wrote under the pen-name "Mark Twain", so as it happens it is true as the actual world turned out that Mark Twain = Samuel Clemens.
By the Principle of the Necessity of (true) Identity, it follows that
Mark Twain = Samuel Clemens at every possible world.
Surely, though, the writings attributed to Mark Twain could just as easily have been penned by, say, Abraham Lincoln. Indeed, it is possible that Abraham Lincoln wrote "Huckleberry Finn" under the pen-name "Mark Twain" while Samuel Clemens held the presidency during the Civil War, which is just to say, it seems, that there exists a possible world where Mark Twain = Abraham Lincoln, contrary to the Principle of the Necessity of Identity.
What is going on here? Remember that not every expression is a rigid designator--only some are. Proper names like "Titanic" and "Samuel Clemens" and natural kind terms like "elm" and "water"--so-called 'mass-terms' or 'collective nouns'--are rigid designators, but definite descriptions like "the author of 'Huckleberry Finn'" are not.
So when we conclude that Abraham Lincoln could have been Mark Twain and not Samuel Clemens from the intuition that Abraham Lincoln could have been the author of "Huckleberry Finn", we mistakenly treat
the author of "Huckleberry Finn"
as a name which can be replaced with
Mark Twain
Yet Mark Twain could not have been Abraham Lincoln since "Mark Twain" has the reference it has as we use it at the actual world. Thus
Mark Twain = Samuel Clemens
at every possible world, since it is our linguistic practice that fixes the reference of the names. Remember, since these are rigid designators, neither intension nor idea nor sense mediate their reference. Accordingly,
Mark Twain = Samuel Clemens
has exactly the same content as
Samuel Clemens = Samuel Clemens
That
Mark Twain = Samuel Clemens
is thus an a posteriori necessary truth. It is necessary if true, but we must discover whether it is true (at the actual world). We can give a fairly straightforward argument for the Principle of the Necessity of Identity as follows:
An Argument for the Principle of the Necessity of Identity
Let 'X' and 'Y' be rigid designators, and suppose X = Y.
Suppose, for purposes of reductio ad absurdum, that possibly, X ≠ Y. That is, X = Y, but suppose it could have been otherwise.
Deploying modal semantics, we have it that X = Y at the actual world, but X ≠ Y at some possible world. Call the world at which X ≠ Y 'w'.
Since X = Y at the actual world and X ≠ Y at w, either 'X' or 'Y' at w denotes a different object at w than the object 'X' (and 'Y'!) denote at the actual world.
By hypothesis, though, 'X' and 'Y' are rigid designators: They refer to the same object at every possible world. (Remember, 'X' and 'Y' are as we use them, as our sociolinguistic culture has determined they be used.)
Hence the proposition that X ≠ Y at some possible world directly contradicts the hypothesis that they are rigid designators.
It follows by reductio that if 'X' and 'Y' are rigid designators and X = Y, then necessarily X = Y.
Having justified the Principle of the Necessity of Identity, we may turn to a series of examples:
- Since Mark Twain = Samuel Clemens and "Mark Twain" and "Samuel" directly refer or rigidly designate Samuel Clemens (the person), the statement "Mark Twain = Samuel Clemens" asserts nothing more than the statement that "Samuel Clemens = Samuel Clemens" asserts, even though it may well be a discovery that Mark Twain = Samuel Clemens.
- Similarly, it was a discovery that Hesperus = Phosphorus, yet "Hesperus" and "Phosphorus" are rigid designators, so it could no more have been the case that Hesperus ≠ Phosphorus than that Venus ≠ Venus (and for the same reason!)
- Finally, heat = the motion of molecules, so heat could not have been anything other than the motion of molecules. Our intuition that heat could have been something other than the motion of molecules rests, Kripke thinks, on confusing heat with the feeling of heat. Surely the feeling of heat could have been caused by something other than the motion of molecules, yet heat itself, irrespective of the feeling of heat by which we ordinarily experience heat, just is the motion of molecules, and necessarily so.
One more example. Suppose pain = c-fibre nerve stimulation. Then pain = c-fibre nerve stimulation at every possible world, since "pain" and "c-fibre nerve stimulation" are rigid designators. Nevertheless, it is clearly conceivable that pain ≠ c-fibre nerve stimulation. If it is conceivable that pain ≠ c-fibre nerve stimulation, then it is possible that pain ≠ c-fibre nerve stimulation. But if there is a possible world at which pain ≠ c-fibre nerve stimulation, then it is not the case that pain = c-fibre nerve stimulation at every possible world. And if it is not the case that pain = c-fibre nerve stimulation at every possible world, then pain ≠ c-fibre nerve stimulation at the actual world, by the Principle of the Necessity of Identity.
Why, though, aren't we making the same mistake with pain we made with heat? It's simple: Unlike heat, pain just is the feeling of pain. We cannot mistake the feeling of pain for pain because the feeling of pain is pain, full stop.
Generalizing, we can say that if the philosophical zombie--a microphysical duplicate of me who is behaviorally indistinguishable from me yet lacks phenomenal consciousness--is conceivable, then it is possible. If the philosophical zombie is possible, then phenomenally conscious (mental) states are not physical states at the actual world, which is just to say that they are not in fact physical states.
Such, at any rate, is the problem posed by the modal argument for physicalism. Next time we take up a response to the modal argument which appears to raise a third challenge to physicalism and the possibility of our understanding the mind vis 'a vis Dretske's Dictum.
Since the various steps in this argument probably (well, most definitely) went by too fast in class to follow, I'll begin by recounting them so as to lay out the argument as best I can.