Message-Id: <199602060300.FAA02067@xiron.pc.helsinki.fi>
Date:         Mon, 5 Feb 1996 18:44:13 -0800
Reply-To: "John E. Clifford" <pcliffje@CRL.COM>
Sender: Lojban list <LOJBAN@CUVMB.BITNET>
From: "John E. Clifford" <pcliffje@CRL.COM>
Subject:      tech: logic matters
To: Veijo Vilva <veion@XIRON.PC.HELSINKI.FI>
Content-Length: 2878
Lines: 60

lobab:
how about reversing the
meanings and having "ro" NOT have existential import (any?) and rosu'o
be the version with existentiual import (every?)
i,n:
This was essentially what I proposed at some point.  It appears that
pc is not happy with this idea.
pc:
Right.  Why have two forms when the special nature of one of these
notions is rarely, if ever, going to be used, and the language has
already dealt with all the significant issues several times over?
Worse, of course, why use the short form for the one you'll never
need?  Decide what it is you want to say, please, then look at the
forms available in Lojban and tell me which one it is you cannot say
using those forms.  If you find one (other than a case where the
whole universe of discourse might be empty), let me know and then
we can talk about what needs to be done.   For now, I get the distinct
impression that you haven't a clue what you're talking about nor what
Lojban allows you to do.

x:
This choice makes SoP have no import, which means that "Some S isn't P"
is true in the absence of S's.
pc:
Well, yes.  But "Some S isn't P" is a conventional reading of a logical
formula and no more to be taken as literal English than "All S is P,"
is.  The correct reading (since Aristotle's time, or at least his
immediate successor's) is just too complex: "If there are S's then
some of them fail to be Ps."  But, of course, the olden guys could get
away with assuming that there always were S's so it didn't matter
much. And, indeed, we don't use that corner much.

x:
To me, the fact that, with that choice, SaP is not equivalent to SeP'
is a drawback, not a plus. It means that it becomes very difficult to
pass negations through quantifiers in order to obtain easier to
understand expressions.
pc:
Well, some folks like obversion.  If they do, they can always shift
over to the other forms, which are actually often simpler in Lojban,
and fiddle there.  (0xSx)xPx is provably exactly equivalent to
Ax:Sx => ~Px, _no da poi broda cu brode_ means  _ro da cu ganai
broda gi naku brode_.  Not obviously a lot more complicated than
the move from _noda cu ge broda gi brode_  or _naku su'o da cu ge
broda gi brode_ for example.

x:
But I agree that in the end it is a matter of taste. There is no
pre-defined right answer. You may think that one choice is preferable
on technical grounds, but there is no logical requirement for that
choice. Before, I had understood you to say that we didn't really have
the choice.
pc:
Well, I tend to think functional completeness is a a logical reason, but
that may be just me.  In any case, we don't have to make a choice, because
Lojban (indeed modern logic) has both systems.  Use whichever you like or
mix and match, just notice what you are doing.  And don't say that
something isn't true in one when you mean the other or are getting them
totally mixed together.
pc>|83