Fourth tense & "third" logic value(s).

[Jeff Prothero <cbmvax!uunet!milton.u.washington.edu!jsp>]

Carl Burke comments:

> As I understand it, this debate which has been clogging my in-basket
> is raging over whether or not to incorporate a fourth "time" cmavo,
> for a set of "past, present, future, and *not applicable*".  The
> fourth tense refers to (in a relativistic sense) events outside the
> perceptible area of space-time; *fourth tense* events cannot possibly
> interact with the speaker, at least in the location/interval in
> question.  Is this an adequate non-technical summation?

An excellent summation, except I prefer "*other*" to "*not
applicable*".  "*Not applicable*" suggests that the statement cannot
sensibly be evaluated in context -- in computer terms, that it
deserves a "compile error" (or evaluates to "bottom".)  But it is not
senseless to discuss nonpresent, nonfuture, nonpast events in a
neighboring galaxy -- it just requires a fourth tense.

Certainly, we could concievably abuse a "*not applicable*" flag by
using it instead of a fourth tense, but this would be a semantic mess.
If someone asks what tense correctly describes the relationship
between pride and the color green, *then* I would invoke *not
applicable*, since pride and green are not spacetime events
describable by tenses.

> This seems to be a useful concept, but it would find applicability
> outside the strictly physics-related relativity frame.  For example, a
> criminal's alibi is an attempt to assert a *fourth tense* relation
> with the crime, under the prevailing conditions.  Locked room
> mysteries, by limiting the communications means, isolate the
> "world-line" of the crime; the detective must identify the means by
> which communication occurred to reach the goal of "solving the case".
> In the limit, barring FTL communications a la Bell's Theorem, you have
> the cases argued (ad nauseum) so far.

(Bell's Theorem / EPR demonstrates "nonlocal effects", but does not
give us FTL communication. Let's not thrash *that* out here!  But I'll
nominate it for best example of the universe being stranger than we
could have imagined...)

Certainly, a literal tense-four relationship to a crime would be an
excellent alibi -- for example, showing that you were born in the
oblivious zone of the crime would be as good as showing you were born
after the crime.  But a locked room doesn't mean much to a physicist:
neutrinos, gravity waves etc freely carry information into and out of
human rooms. (A black hole, now, ...)  Such a use of the fourth tense
would be very loose and analogical.  In English, at least, I have the
impression that such loose use of the tenses themselves is rare to the
point of non-existence, although the corresponding predicates are fair
game.

> This would appear to be every bit as useful as the addition of a third
> value to traditional Boolean logic: True, False, *unask the question*.

I think there are actually a number of candidates for a "third"
logical value: "unknown" springs to mind, plus "true but unprovable"
and "orthogonal -- can be assumed true *or* false without danger of
contradiction or inconsistency". I suspect pc could provide a dozen
more.  Want to make up a list and run them by RLC?  They deserve at
least compound predicates, I should think.

> The third value holds where neither a true or false value is
> applicable; the traditional question is "When did you stop beating
> your wife?"  I seem to recall that there is another way to assert this
> third truth value in Lojban, but I do not recall the method.  If this
> is available, then there is no need (other than shorthand convenience)
> for the fourth tense; you merely state that *neither true nor false*
> *actor* *relation* *arguments* ***at all times/places, if you must
> specify***

The entire Lojban tense/locator system is (as RLC likes to remind us)
a shorthand convenience for things we could say via (appropriate)
predicates, and one can certainly handle the fourth tense this way,
with or without a third logic value.  But you lose symmetry,
compactness and compound tenses involving the fourth tense -- you add
enough verbosity to practically guarantee that nobody will actually
use the fourth tense: "Omit needless words! Omit needless words! Omit
needless words!" (Will Strunk.)

> Maybe this will breathe yet more life into this maelstrom.  Maybe not.

Or maybe it will spawn a separate third-logic-value thread? :-)

> Carl Burke    m16569@mwvm.mitre.org
> My opinions are my own, and are *True/False* held by my employers.
> *
> *        Carl

Thank you for sharing them,

-- Jeff (jsp@milton.u.washington.edu)