1. Text # 1: Brains
Danilo Dantas
January 23, 2013
In page 79, Olson presents an argument (the thinking brain problem) supporting the brain view :
(1) There is such a thing as my brain.
(2) My brain thinks my thoughts in the strictest sense.
(3) If my brain thinks my thoughts in the strictest sense, then anything else that thinks my
thoughts does so in the derivative sense of having a part that thinks in the strictest sense.
(4) If anything thinks my thoughts in the strictest sense, I do.
∴ I am my brain.
At first glance, the argument doesn’t need premise (1), but I think that this is really not the case.
I think that premise (1) makes two important claims to the argument: (i) an existential claim, and a
unity claim. This unity claim is very important because it avoids a contradiction with premises (2),
(3) and (4). This is the formalization ( = XOR, strict/derivative thinker are about my thoughts):
(1) ∃x(myBrain(x) ∧ ∀y(myBrain(y) → y = x)).
(2) ∀x(myBrain(x) → strictThinker(x)).
(3.1) ∀x(Thinker(x) ↔ (strictThinker(x) derivativeThinker(x))).
(3.2) ∀x(strictThinker(x) → ∀y(x = y → ¬strictThinker(y))).
(4) ∀x(strictThinker(x) → x = me)
∴ myBrain(me).
The point is that, without premise (1), we can generate a contradiction from premises (2), (3),
and (4) and suppositions of the same kind of two brains:
myBrain(b1 ) ∧ myBrain(b2 ) ∧ b1 = b2 (Two brains)
This would be the reasoning:
• From the supposition and (2), we can derive strictThinker(b1 ) and strictThinker(b2 ).
• From this result and (3.1) and (3.2), we can derive ¬strictThinker(b1 ) and ¬strictThinker(b2 ).
This already generates a contradiction.
• From this result and (4) we can derive me = b1 and me = b2 .
Which also generates contradictions with b1 = b2 .
This is the importance of premise (1) in the argument: in addition to make the existential claim
and let premise (2) being existentially uncommitted, it blocks suppositions of the same kind of two
brains, and ensures that premises (2), (3), and (4) do not generate contradictions.
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