From cbmvax!uunet!milton.u.washington.edu!jsp Fri Mar 1 20:57:46 1991 Return-Path: Date: Fri, 1 Mar 91 17:07:26 -0800 From: Jeff Prothero Message-Id: <9103020107.AA20312@milton.u.washington.edu> To: m16569@mwvm.mitre.org Cc: lojban-list@snark.thyrsus.com In-Reply-To: Carl Burke's message of Wednesday, 27 Feb 1991 16:35:10 EST <9102272133.AA10995@mwunix.mitre.org> Subject: Fourth tense & "third" logic value(s). Status: RO 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)