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C00002 00002	Minor
C00005 00003	How moods affect reasoning
C00009 00004	My explanation
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Minor

Remarks about holograms.  If someone else says something similar,
please excise mine.

abstract - It is true that mental processes are not mainly described
by equations.  Neither is digestion or the habits of bees.  I.e.
cognitivism is not revolutionary in that respect.

5 I agree that %2systematic%1 explanations are required.

11 There is a continuum of reductions.  At one end we have the
reduction of thermodynamics to statistical mechanics.  If you know
statistical mechanics, then you can deduce all you want about
thermodynamics, and this deduction is reasonably practical.  In
the middle we have, say, the reduction of computers to structures
built of gates and latches.  You may know all about gates and latches,
but not know what you need to know about computers.  An extreme
example comes from the fact that numbers can be represented by
strings of beads, but he who knows all about beads may still be
puzzled by Fermat's last theorem.

12 The criterion for a device that plays chess can be stated more
rigorously.
How moods affect reasoning

	I agree with Haugeland that moods affect human reasoning in a way
unlike that of adjoining to a collection of sentences expressing one's
beliefs and observations additional sentences describing mood, and then
drawing logical conclusions from the augmented collection.  My explanation
invokes a mode of reasoning, called %2circumscription%1, that I have
proposed elsewhere (McCarthy 1977).

	It is often necessary to draw conclusion from insufficient
data, either because a person or program doesn't have all the data
or even because one's "mental capacity" is too small to take into
account all the data one has.  We propose that this is often done
by assuming that the entities whose existence is implied by the
facts one is taking into account are all the entities that exist
in certain categories.  For example, one may presume that the
advantages one has listed of a certain course of action are all
the advantages there are.  That these are all the advantages does
not follow from the individual sentences asserting that each of
them is an advantage.  We call %2circumscription%1 the mental
operation of presuming that an explicit list of objects exhausts
a class.  Various ways of formalizing it are discussed in the
reference.

	Circumscription is a powerful but unsafe mode of reasoning.
It is powerful in that it allows deciding what to do in cases
where a decision is necessary but information is insufficient.  It
is unsafe, since additional entities of the circumscribed classes
may actually exist.

	We propose that moods affect reasoning by affecting the class of
facts taken into account.
For example, a melancholy mood could directly retrieve facts
that have previously been classified as melancholy.  On the other
These sentences could in turn excite an information retrieval
mechanism to produce associated sentences.  This could even be
done by injecting a single %2I feel melancholy%1 sentence, although
this seems unlikely.
My explanation
is related to mechanisms for jumping to conclusions from insufficient
data.  In (McCarthy 1978), I propose a mechanism called %2circumscription%1
for doing this, and for the present let us regard it as a %2competence%1
explanation, i.e. it gives the result of a mental process without
asserting that the human brain goes through the same steps.
%2Circumscribing%1 a collection of sentences is jumping to the conclusion
that the objects in a certain class whose existence is inferrable
from the collection of sentences exhaust the class.
In the paper, I argue that without such a mechanism, it would hardly
ever be possible for a human or machine to draw conclusions from
the data that is actually available in common sense situations.