**From:** Russell Wallace (*russell.wallace@gmail.com*)

**Date:** Thu Sep 15 2005 - 14:11:54 MDT

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On 9/15/05, Eliezer S. Yudkowsky <sentience@pobox.com> wrote:

*>
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*> Actually, I also need to specify that at least one nonblack object is
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*> known to exist in every possible world; along with the requirement that,
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*> in at least one possible world containing nonblack ravens, the ratio of
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*> these nonblack ravens to all other nonblack objects does not approach
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*> zero; and the requirement that the proposition "All ravens are black"
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*> not initially have prior probability equal to zero; in order for my
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*> general conclusion to hold that randomly sampling a nonblack object and
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*> finding it to be a nonraven ALWAYS increases the probability assigned to
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*> the proposition "All ravens are black." (Assuming I haven't missed any
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*> other necessary assumptions.)
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*>
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You also need to assume the world has no structure.

Suppose in real life you looked around at random, saw a white speck, and on

closer inspection found it to be a white crow. That's a nonblack nonraven,

but it would actually count as strong evidence _against_ the proposition

that all ravens are black: crows and ravens are closely related, and if the

one species can produce the occasional albino, the other probably can too.

- Russell

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