The Modal Argument

Review: The “Hard Problem” Remember that there are three arguments that make

consciousness a ‘hard’ problem.

1. Knowledge Argument2. Modal Argument3. Explanatory Gap Argument

Hard Problem: we do not know how to go about solving it; isolating neural or computational mechanisms is not enough.

1. The Knowledge Argument P1: Physicalism says that all facts are physical facts.

P2: In the room, Mary has complete physical knowledge of color perception.

P3: When she leaves the room, Mary acquires new knowledge (i.e. what it is like to see red).

C: Physicalism if false: there are facts (i.e. about phenomenal properties) which escape the physicalist story.

Response #1 P3? Churchland maintains

that this is possibly false.

We do not understand as much about the brain as Mary does.

So perhaps Mary would say (when shown tomato) “Ahh, just as I thought”.

Response #2 Equivocation? What does it mean to say that Mary

gains “new knowledge” when she sees the tomato?

Churchland argues that, even if Mary does acquire new knowledge, this does not mean that there are facts that escape physicalism.

Mary merely gains a new way of knowing old facts.

Worry Are Churchland’s responses consistent?

It seems that his response to Jackson is that (a) Mary would know, before release, what it is like to see red – and – (b) Mary would learn what it is like to see red, but this new knowledge would not undermine physicalism.

Charitable reading: Mary might very well know, but even if she doesn’t, it would not undermine physicalism.

2. Modal Argument Today we turn to the

second argument in the trilogy.

This argument was presented by Saul Kripke (b. 1940-) in a series of lectures he gave at Princeton in 1970.

Zombies Kripke’s argument is

based upon what philosophers have called the “zombie hunch”.

So let us be clear: philosophical zombies are nothing like Hollywood zombies.

Hollywood Zombies Hollywood zombies are

reanimated dead-people who like to eat human flesh.

They often have strange behavioral features (they usually walk slowly and awkwardly, although in 28 Days Later they run really fast).

Philosophical Zombies They look and behave just

like you and me.

But their defining feature is that they do not have any consciousness.

So as philosophical zombie is physical identical to a normal human being, but there is nothing it is like to be them.

Challenge to Physicalism Question: Why are philosophers worried about such

Zombies?

Answer: They are a serious threat to Physicalism. Physicalists cannot allow that you can have a zombie twin which is physically identical to you but who lacks consciousness.

If all properties are physical properties, then someone who shares all your physical properties must have the same consciousness.

The Zombie Argument A thumbnail sketch of the argument might

look something like this…

P1: Physicalism says that all truths are physical truths.P2: Zombie twins are possible.C: Physicalism is false.

Physicalist response? It is tempting to say, in response, that this merely

shows that mind-body identity is a contingent truth.

(Note: This is what JJC Smart says in response to the objection that we can conceive of being turned to stone, yet feel pain).

To make heads or tails of this response, we need some modal terminology….

Modality Talk of ‘modalities’ refers to the way we qualify the truth of judgments

with respect to possible worlds.

Possible world: maximally complete (i.e. leaves out no information) consistent (i.e. non-contradictory) set of facts about the world. 

Contingent truths: These are truths that are true in some worlds, but false in others.

Necessary truths: These are truths that are true in all worlds.

So the temptation is to say that ‘M=B’ is contingently true in our world. Thus, the fact that we can imagine zombies only shows that there are other worlds in which the identity does not hold.

Kripke on A Posteriori Necessity Kripke argues that this is a mistake. He

maintains that natural kind terms such as ‘pain’ and ‘c-fiber firing’ are rigid designators that have the same reference in every possible world.

This entails that the following premise is true:

P1: If M=B, then NEC (M=B).

Clarifications It is contingent that mean kinetic energy causes

sensation of heat; but it is necessary that ‘physical heat = MKE’.

We often think that this theoretical identity is contingent because it is a posteriori (it required experience and scientific method to discover it).

Philosophers used to think that all necessary truths were analytic; but Kripke convinced most people that there are a posteriori necessary truths.

The Modal ArgumentP1: If ‘pain = c-fiber firing’, then NEC (‘pain = c-fiber firing’).

P2: We can conceive of zombies whose c-fibers are firing but who do not feel pain.

P3: Conceivability entails metaphysical possibility.

P4: Zombies are metaphysically possible.

C: It is false that ‘pain = c-fiber firing’.

Kripke’s Blocked Move Kripke recognizes that physicalists might offer the

following move: we can explain away the zombie hunch and deny P4.

How so? Because it also seems possible that we could have water without H20. But they are necessarily identical. So we cannot trust such hunches. They are just ‘modal illusions’.

Question: Why does Kripke maintain that this strategy will not work in the case of pain?

Kripke’s Blocked Move

Kripke’s Blocked Move Kripke agrees that materialists can explain away the “water

hunch”. But this will not work for the case of pain.

The reason is that we recognize instances of WATER through their accidental features. It just so happens that water appears to us as clear, etc. But it might appear differently to creatures on Mars.

But we cannot say this with PAIN. We recognize pain through its essential property. If it didn’t hurt, it would not be pain!

Hill’s Reply Question: How does

Hill respond to Kripke? Does he manage to avoid the block?