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mental.abs[e85,jmc]	Abstract for Halpern based on mental situation calculus
"halpern.ibm-sj"@csnet-relay,val/cc
abstract for knowledge conference
I don't know whether you are still planning to have me as an invited
speaker.  But anyway here is an abstract of a submitted paper, which
is far from ready, but I think it will be interesting and new.
The paper may turn out to be joint with Vladimir Lifschitz.  I'll
be away for a week.

Mental Situation Calculus

	The situation calculus of (McCarthy and Hayes 1969) has mainly
been used to reason about states of the physical world, taking into
account the locations and physical properties of objects and admitting
such events as moving them.  Analogously we can consider a {\it mental
situation calculus} (MSC) in which the situations include beliefs,
goals, intentions and other mental qualities, and the events include
inferring, observing, establishing goals and discharging them.

	MSC has several motivations.

	1. MSC involves reifying beliefs, and one of its basic
forms will be  believes(<proposition>,ss)  standing for the assertion
that the proposition is believed in mental situation  ss.  The formalism
allows for belief not to be closed under inference.  In fact one of
the possible mental actions is to make an inference.  Therefore, we
can describe in detail the circumstances under which we want our
system to make inferences.

	2. Non-monotonic reasoning requires closer control over
inference than deduction, because of its tentative character.
Some problems that have recently arisen with blocks world axiomatizations
may require that circumscription be controlled in accordance with
with the pedigree of the system's objective beliefs and not merely being
determined by what the beliefs are.

	3. It looks like several useful methods of control of reasoning
can be accomplished by hill-climbing in mental situation space.

	Besides reifying beliefs, MSC involves reifying goals and
partial plans for achieving them.

	Depending on progress the paper to be presented will include
both general discussion of MSC and specific formalizations.