A person's state of mind cannot be adequately regarded
as the set of propositions that he believes--at least not if
we regard the propositions as sentences that he would give
as answers to questions. For example, as I write this I
believe that George Bush is the President of the United States,
and if I were entering information in a database, I might
write
Our proposal is to use a database consisting entirely of outer
sentences where the pedigree of an inner sentence is an auxiliary
parameter of a kind of
modal operator surrounding the sentence. Thus we might have the outer
sentence
The use of formalized contexts provides a convenient way of
realizing this idea. In an outer context, the sentence with reasons
is asserted. However, once the system has committed itself to
reasoning with the proposition that Bush is President, it enters an
inner context with the simpler assertion
Consider a belief revision system that revises a database of beliefs solely as a function of the new belief being introduced and the old beliefs in the system. Such systems seem inadequate even to take into account the information used by TMS's to revise beliefs. However, it might turn out that such a system used on the outer beliefs might be adequate, because the consequent revision of inner beliefs would take reasons into account.