Re: Non-black non-ravens etc.

From: Michael Wilson (
Date: Mon Sep 12 2005 - 12:06:52 MDT

Richard Loosemore wrote:
> Interestingly enough, a real thinking system would respond by noting
> that the question of whether all ravens are black is best answered,
> not by fabulously complex appeals to probability theory, but
> to some background understanding of what makes them black - genetic
> characteristics.

Something is seriously broken if you think that probability theory is
'fabulously complex' compared to nearly any causal explanation, never
mind one as sophisticated as genetics. On the contrary, probability
theory is extremely simple; the only reason humans find it hard is
because it can be highly counter-intuitive. The total process of a
human applying probability theory /is/ fabulously complex, but this
need not be true for an AI, as I will detail below;

> Real thinking systems, in practice, obviously cope with the task of
> gathering new knowledge by little strategies and appeals to connected
> knowledge... (I) don't yet have a clear reason to believe that Bayesian
> inference would be necessary or useful or even applicable at that base
> (local mechanisms) level,

I'm not sure that you have a clear idea of how advocates of rational
cognition are proposing that mechanisms be layered. I have often shot
down armchair critics of AI for confusing the fact that humans implement
logical inference as a high level, symbolic process (supported by
grounded concepts and all sorts of complex lower-level mechanisms),
while AIs may implement logical inference as a low-level mechanism (and
indeed, all AIs on current hardware are ultimately based on boolean
logic). I'm not certain, but it looks like you're making the same kind
of mistake; an AI can support 'irrational'/'fuzzy'/'intuitive' sorts of
cognition as a layer above a logical substrate, and then possibly even
another layer of high-level logical inference above that. Your criticism
would apply if probability theory was being used the way humans use it,
as a layer above concepts, grounding etc, or the way that GOFAI might
use it, i.e. on its own without any of the other necessary complexity,
but it is inapplicable as a criticism of Bayes as the underlying basis
for cognition. You are correct that rationally based cognition has not
been shown to be tractable, but I addressed that in an earlier reply.

 * Michael Wilson

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