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What software does this nice html indented formating? I can't
maintain it.
On Jan 18, 2008, at 8:28 AM, Chris Menzel wrote:
On Jan 17, 2008, at 10:38 PM, John Black wrote:
...
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
cm> Small point of logical terminology -- "tautology" is reserved for
logical *truths* of propositional logic.
Ok. I'll watch out for that.
jb>
because there is no other context, which if it took the place of "today",
would change the value of that tautology. This is pragmatic, to count as a
context it must make a difference, and there must be an alternative context
that makes a different difference.
cm> So you appear to be saying that logical truths and logical
falsehoods can never legitimately be asserted to be true or false in a context
because their truth values never change. Trouble is, there is no general
algorithm for saying when a sentence is a logical truth or a logical falsehood
so no general way to be sure when it's ok to use "ist". Why not just say
that logical falsehoods are false in (and logical truths true in) every
context rather than trying to spell out when a context is or is not valid for
a given proposition? What's the harm?
I see your point, probably no harm. I think what I was
thinking of was trying to narrow the use, and thus try to eliminate some of
the problems of an overly broad application of
"context".
jb>For
example, to me right now, 'yesterday' is a valid context, because I can
think of things that are different between that interval and 'today'. But
'yesterday-10:32am-to-10:42am' is not a valid context because I cannot
think of anything (without further investigation) that falls into that
particular interval.
cm>So what counts as a context is dependent on someone's ability to
remember something that happened during the interval in question? If so,
you seem to be wanting ist to be a 3-place relation that includes a parameter
for an agent: (ist c John A) -- "John recalls that A is true in context c", or
the like. But if so, then what you *really* need is a 4-place relation
(ist c John t A) that includes a time parameter -- "John recalls at time t
that A is true in context c" -- since of course you might come to recall
something (after further investigation) at some later time t that occurred in
context c that you don't remember at an earlier time. That doesn't strike me
as a sense of context that is of much use for knowledge
engineering.
Well, I can see the humor in your spoofing of that ideas,
and it does seem like it could reduce it to near absurdity. But never
underestimate the need for specialized kinds of applications of technology.
The 4-place relation you describe, (ist context agent time proposition),
sounds like something that may be valuable in legal reasoning, where who knew
what when is critically important.
But there is an even more important thread that I want to
develop, as time permits, in the next few weeks, that has to do with the idea
that context is really a biological concept, along the lines of Ruth Milikan
in | Language, Thought, and Other Biological Categories
| http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=5994.
John Black
www.kashori.com
Chris Menzel
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