On Jun 17, 2014, at 9:08 AM, David Whitten <whitten@xxxxxxxxxx> wrote: (01)
> I would like to point out that using July as a time is problematic, (02)
I entirely agree, but didn't want to complicate my response by going into to
many issues at the same, er, time. (03)
> as I believe that:
>
> (cl:comment 'C employs P during time interval T'
> (employs C P July)
> )
>
> would say that July is a time interval.
> To my way of thinking, July is the name of the (infinite) set
> of all time intervals that can be classified as overlapping with
> the month of July in any year. (04)
A class of time intervals, in other words. Makes sense. There are other
approaches, of course, but for sure, one needs to have a carefully thought
through ontology of times and intervals and dates, and stick to it carefully.
Just using words like "July" and hoping for the best, is not going to work. (05)
>
> Thus, the statement (employs IBM Fred July)
> says that IBM employs Fred during the month of July in
> every possible year. (perhaps Fred is a seasonal worker)
>
> This is a different statement by far than saying IBM employs
> Fred for a particular month of July in a particular year.
> I expect also that the 3-D vs 4-D time view would argue
> that it is actually a time-slice of Fred that is employed rather
> than the Fred that exists at all times. (06)
I have come to think that the blood spilled over this 3d/4d contrast is not
worth the cost. We all agree that things like persons last through time while
retaining their identity: I am the same person now as I was ten years ago.
Exactly how you reconcile this with the other obvious fact that things change
with time, is really only a matter of notation. If you prefer to write the time
parameter as attached to relations or predicates, and think of properties
changing with time, then that is one way to do it (often called 3-D); if you
prefer to attach the time parameter to object names and think of this as
time-slices of things, that is another (4-D). But it is straightforward to
translate between these, and with an expressive enough logic (such as ISO
common logic) even to state their equivalence using axioms. As long as we all
keep our philosophers on a short leash and stop them snarling at one another,
we should have no trouble. (07)
Pat Hayes (08)
>
> David Whitten
> 713-870-3834
>
>
>
>
> On Tue, Jun 17, 2014 at 7:51 AM, Tara Athan <taraathan@xxxxxxxxx> wrote:
> On 6/17/14 1:03 AM, Pat Hayes wrote:
> >> Using the IKL “that” operator and a “during” relationship and the concept
>“July” (a ‘calendar month’):
> > Whoa. No, this is NOT the right way to do it. In fact, this is meaningless.
>According to the IKL semantics, (that (employs C P)) denotes a fixed
>proposition which is true or false. There is no room for any time-dependent
>variability in its truth value, or for making it depend on some other
>parameter.
> >
> It may not be the *best* way to do it, but I don't agree that it's wrong
> or meaningless. Using the proposition (that (employs C P)) as an
> argument in a relation is not obstructed by its denotation of a fixed
> proposition which is true or false (in any given interpretation).
>
> Starting off without quantifiers:
>
> (cl:comment 'C employs P'
> (employs C P) )
>
> (cl:comment 'It holds during time interval T that C employs P'
> (during (that (employs C P)) T )
>
> Nothing wrong with that - the truth values of these sentences are
> independent of each other.
>
> Now bring on the quantifiers to relate the two
>
> (forall C P
> (if
> (cl:comment 'C employs P'
> (employs C P) )
> (exists T
> (cl:comment 'It holds during some time interval T that C employs P'
> (during (that (employs C P)) T )
> ) ) )
>
> Some users may find this clearer than the polymorphic representation.
> Why not let them use it?
> It is still possible to have the polymorphic representation behind the
> scenes for reasoning purposes.
> (forall C P T
> (iff
> (cl:comment 'It holds during time interval T that C employs P''
> (during (that (employs C P)) T )
> (cl:comment 'C employs P during time interval T'
> (employs C P T)
> ) )
>
> Also, using the "that" operator for temporal context is a gateway to
> using it for other contexts/modalities.
> I find the symmetry appealing:
> (cl:comment 'It holds before time interval T that C employs P'
> (before (that (employs C P)) T)
> (cl:comment 'It holds after time interval T that C employs P'
> (after (that (employs C P)) T )
> (cl:comment 'It is possible that C employs P'
> (possible (that (employs C P)) )
> (cl:comment 'It is forbidden that C employs P'
> (forbidden (that (employs C P)) )
> (cl:comment 'Jane believes that C employs P'
> (believes Jane (that (employs C P)) )
> (cl:comment 'Omar knows that C employs P'
> (knows Omar (that (employs C P)) )
> (cl:comment 'Maria asserts that C employs P'
> (asserts Maria (that (employs C P)) )
> ...
>
> Tara
>
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