Re: momentary and persistent minds

From: Nick Bostrom <>
Date: Sun, 14 Jun 1998 02:07:04 +0000

Wei Dai wrote:

> The biggest problem I see with your interpretation is that it is based on
> brain states, which seems to imply that two brain instances in the same
> brain state must have the same identity.

What I meant (or should have meant) by "brain states" is: instances of
brain states. If two brains are in the same state A, there would be
two instances of the state A. I don't want to claim that these two
instances would necessarily belong to the same observer.

> For example suppose at time 0
> there are two observers in the same brain state and at time 1 one of them
> sees a red light and the other sees a green light. According to your
> interpretation both of them would conclude at time 0 that "I will see red"
> and "I will see green" both have probability 1.

That depends on whether the two brain state instances as time 0
--call them S-a and S-b respectively-- both belong to the same person
as the two brain state instances that exist at time 1 -- RED and
GREEN. Whether this is the case depends on your theory of
personal identity.

Suppose that your theory of personal identity says that all these
brain-state instances belong to the same person P. Then at time 1, P
would *both* observe a green light and a red light. This would be
analogous, perhaps, to split-brain patients. One half of their brain
may have a sensation A and the other half may have the sensation B,
and neither half knows what sensation the other has; yet the patient
(on this theory of personal identity) has both these sensations.

Suppose instead that S-a and S-b belong to different persons, Pa
and Pb respectively, and that RED belongs to Pa, and GREEN belongs
to Pb. Then at time 0, Pa and Pb might not know what they will
experience at time 1, if they can't tell whether they have the brain
state instance S-a or S-b. Even if they know which of these
instances they have, they might still not know what they will
experience at time 1, if they are ignorant as to whether the S-a
belongs to the same person as RED or as GREEN (and similarly for

Nicholas Bostrom
Department of Philosophy, Logic and Scientific Method
London School of Economics
Received on Sat Jun 13 1998 - 18:16:14 PDT

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