The “Explanatory Gap” Where it is said that identity theory is not necessary false, but merely unknowable

Last time: The Modal Argument P1: It seems possible that there are zombies. P2: If mind=brain, then this identity is metaphysically necessary (i.e. it is true in every possible world). P3: We cannot explain away this intuition. P4: If we cannot explain away this intuition, then zombies are metaphysically possible. C: Identity theory is false.

Hill’s Response: Deny P3  Hill exposes an important assumption in Kripke’s argument: that the only way to explain away the ‘zombie hunch’ or ‘Cartesian intuition’ is the way that Kripke describes.  But Hill presents another (unexcluded alternative) way to explain away the zombie hunch: we are not really imagining (p&~q) at all!  Rather, we are perceptually imagining (p) and sympathetically imagining (~q) and then splicing them together. And we have no reason to trust such unreliable spliced modal intuitions.

Levine’s Response: ?  Question: Which premise of Kripke’s argument does Levine challenge?  Everyone hold up a number on the count of three.

Levine’s Response: Deny P4  “For what seems intuitively to be the case is, if anything, merely an epistemological matter. Since epistemological possibility is not sufficient for metaphysical possibility, the fact that what is intuitively contingent turns out to be metaphysically necessary should not bother us terribly. It’s to be expected” (356).  So Levine maintains that you cannot draw strong metaphysical conclusions from the zombie hunch!

Joseph Levine  Levine is a Philosopher of Mind at UMass-Amherst.  He published this extremely influential article in  You can find a bunch of his on-line articles on his webpage.

Levine’s Argument  It should be noted that Levine accepts a great deal of Kripke’s Modal Argument: it seems that he accepts every statement except P4!  Question: How can we build up Levine’s argument from these remaining premises?  Hint: Levine wants to establish a weaker (but still problematic) conclusion against materialism.

Levine’s Argument P1: It seems possible that there are zombies. P2: If mind=brain, then this identity is metaphysically necessary. P3: We cannot explain away this intuition. P4: If we cannot explain away this intuition, then ???. C: Identity theory is ???.

Levine’s Argument P1: It seems possible that there are zombies. P2: If mind=brain, then this identity is metaphysically necessary. P3: We cannot explain away this intuition. P4: If we cannot explain away this intuition, then there is an explanatory gap between matter and qualia. C: Identity theory is ???. (WHAT DOES HE THINK FOLLOWS FROM P4?)

Levine’s Argument P1: It seems possible that there are zombies. P2: If mind=brain, then this identity is metaphysically necessary. P3: We cannot explain away this intuition. P4: If we cannot explain away this intuition, then there is an explanatory gap between matter and qualia. P5: Corollary - If there is an explanatory gap between matter and qualia, then we cannot tell which psycho-physical identity statements are true. C: Identity theory is ???. (WHAT DOES HE THINK FOLLOWS FROM P5?)

Levine’s Argument P1: It seems possible that there are zombies. P2: If mind=brain, then this identity is metaphysically necessary. P3: We cannot explain away this intuition. P4: If we cannot explain away this intuition, then there is an explanatory gap between matter and qualia. P5: Corollary - If there is an explanatory gap between matter and qualia, then we cannot tell which psycho-physical identity statements are true. C: We cannot know, in principle, whether or not materialism about phenomenal consciousness is true.

Crucial Step: P4 P1: It seems possible that there are zombies. P2: If mind=brain, then this identity is metaphysically necessary. P3: We cannot explain away this intuition. P4: If we cannot explain away this intuition, then there is an explanatory gap between matter and qualia. P5: Corollary - If there is an explanatory gap between matter and qualia, then we cannot tell which psycho-physical identity statements are true. C: We cannot know, in principle, whether or not materialism about phenomenal consciousness is true.

Zombie hunches and explanatory gaps  Question: Why does Levine think that the zombie hunch reveals an explanatory gap?

Zombie hunches and explanatory gaps  Levine thinks that (p&~q) seems possible because we do not see any intelligible connection between them.  There are neural correlates of phenomenal consciousness, in other words, but we do not understand why they are paired with such-and-such particular qualia.  So it seems arbitrary that NC1 is correlated with Q1 rather than Q2 or Q3.

Crucial point: this gap does not exist in other material sciences  Levine argues that this explanatory gap is unique to the study of consciousness.  Question: Why does he think that such a gap is not exposed in identity statements such as “heat is mean kinetic energy”?

Crucial point: this gap does not exist in other material sciences  First: The concept of ‘physical heat’ is fully exhausted by its causal roles.  Heat is that (empty slot) which causes the expansion and contraction of the mercury in thermometers, that (empty slot) which causes water to boil (in the relevant conditions), that (empty slot) which causes human beings to feel sensations of heat, that (empty slot) which causes martians to feel sensations of cold, etc.  This reminds one of Armstrong; and it should.

Crucial point: this gap does not exist in other material sciences  Second: In the case of heat, these causal roles are exhaustively explained by the physical entity that fills the open slot. “It is explanatory in the sense that our knowledge of chemistry and physics makes it intelligible how it is that something like the motion of molecules could play the causal role we associate with heat” (357).

Illustration: Water  One of the causal roles of heat is to cause water to boil. His point is that we can see a connection between what happens at the molecular level and what happens at the microscopic level.  Simple version: The kinetic energy of heat causes the water molecules to bounce around more quickly, and when they move fast enough, the water boils.

Levine vs. Armstrong  Armstrong would argue that there is no explanatory gap in the case of pain.  He analyzes pain in terms of its causal roles. And these can be theoretically explained in material terms.  So what is the problem?

Levine vs. Armstrong  Armstrong appears to have left something crucial out of his analysis: the phenomenal conscious experience of what is like to feel pain.  “[W]hat is left unexplained by the discovery of C-fiber firing is why pain should feel the way it does! For there seems to be nothing about C-fiber firing which makes it naturally “fit” the phenomenal properties of pain, any more than it would fit some other set of phenomenal properties. Unlike its functional role, the identification of the qualitative side of pain with C-fiber firing (or some property of C-fiber firing) leaves the connection between it and what we identify it with completely mysterious” (357).

Good and Bad News for Materialism  The good news is that the zombie argument does not demonstrate that materialism is false. It might (for all we know) be true. The zombie hunch turns out to merely involve an epistemic gap.  The bad news is that the explanatory gap leaves us with an epistemological problem that is serious in its own right: we really don’t understand the relationship between consciousness and the brain. The connection between them is mysterious.

Crucial step: P5 P1: It seems possible that there are zombies. P2: If mind=brain, then this identity is metaphysically necessary. P3: We cannot explain away this intuition. P4: If we cannot explain away this intuition, then there is an explanatory gap between matter and qualia. P5: Corollary - If there is an explanatory gap between matter and qualia, then we cannot tell which psycho-physical identity statements are true. C: We cannot know, in principle, whether or not materialism about phenomenal consciousness is true.

The Corollary  Definition of ‘corollary’: “A proposition that follows with little or no proof required from one already proven”.  Question: Why does the explanatory gap problem entail that the truth of psychophysical identity statements is unknowable?

Groupwork  Why does Levine think that the explanatory gap thesis has this corollary?  Do you agree that it does? Why or why not?