The Starting Argument in the Zombie Attack

Selmer Bringsjord

10/6/97

• Your brain starts to deteriorate and the doctors replace it, piecemeal, with silicon chip workalikes, until there is only silicon inside your refurbished cranium.
• ASearle, at least three distinct possibilities arise:

  V1

  The Smooth-as-Silk Variation:

  V2

  The Zombie Variation:

  V3

  The Curare Variation:

Searle wants to draw a certain conclusion from V2:

In [V2] we imagined that the mediating relationship between the mind and the behavior patterns was broken. In this case, the silicon chips did not duplicate the causal powers of the brain to produce conscious mental states, they only duplicated certain input-output functions of the brain. The underlying conscious mental life was left out ([3], 68).

And here is Dennett's reaction:

But that is only one of the logically possible interpretations of his second variation The other is the crucial one: while you are dying, another consciousness is taking over your body. The speech acts you faintly hear your body uttering are not yours, but they are also not nobody's! I cannot see how Searle could simply have overlooked this gaping loophole in his thought-experiment. But there it is I am baffled ([2], 198-9).

But what exactly does Searle want from V2? He tells us explicitly on page 69 of The Rediscovery of the Mind that he wants to establish via V2 and V3 that a certain trio of propositions is inconsistent. The trio, reproduced verbatim (p. 69):

(1)

Brains cause conscious mental phenomena.

(2)

There is some sort of conceptual or logical connection between conscious mental phenomena and external behavior.

(3)

The capacity of the brain to cause consciousness is conceptually distinct from its capacity to cause motor behavior. A system could have consciousness without behavior and behavior without consciousness.

Represent the three propositions using elementary logical machinery: Bx iff x is a brain; Mx iff x causes (a full range of) mental phenomena; and Ex iff x causes (a full range of) external behavior. Then the trio, with Searle's underlying modal notions brought to the surface, and a denoting the brain of the character in our thought-experiments, becomes

(1 )

(2 )

(3 )

The set {(1 ), (2 ), (3 )} is provably inconsistent, in garden variety contexts; the proof is trivial, for example, in quantificational S5 (which I happen to like) and the weaker T.

Proof. Proposition (1 ) is superfluous. Then, e.g., instantiate appropriately on axiom- schema T to get, with (2 ), by modus ponens, ; instantiate to , derive by propositional logic that , rewrite this by the rule known as necessitation to , and in turn rewrite this as , and then, by double negation, as , which of course contradicts (3 )'s first conjunct.

• Dennett's objection, however, is that (3 ) doesn't follow from V2.
• So let V2 denote the one-(moribund)consciousness variation Searle describes, let V2 describe the two-consciousness variation Dennett describes (and, for that matter, let V2 denote the three-consciousness case, V2 the four, ad infinitum).
• Clearly, V2 (as Dennett himself concedes in the quote above).
• And just as clearly this logical possibility implies the second conjunction of (3 ) (and V3 implies the first conjunction).

• Now, Searle's ultimate aim is probably not to show {(1), (2), (3)} or its formal correlate inconsistent, for reaching this aim, as we have seen, is a matter of some pretty straightforward logic.
• Rather, Searle aims no doubt to refute the claim that there is a conceptual connection between conscious mentality and behavior, that is, he seeks to demonstrate the truth of (3 ) and the falsity of (2 ).
• This is a result which follows when the inconsistency we have noted is combined with V2 , V3 and (( V2 V3 ) (3 )).

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