on Thur. Jan. 17, 2008, at 11:38, John Black
JB>In other words, my intuition says that in
this case: (ist today (and A (not A))), today is not a valid context for that
tautology because there is no other context, which if it took the place of
"today", would change the value of that tautology.
I just realized that if A = "(President JimmyCarter)" and the
time interval was 'time-interval:1950-2000' then A would in fact be both true
and false within that interval - just at different times points or intervals
within that interval. In other words:
(ist time-interval:1950-2000 (and
(President JimmyCarter) (not (President JimmyCarter)))).
So today is is a "valid context" (if there is such a thing)
since there are other intervals that make that proposition true.
I'm going back to more reading and thinking.....