LINGUIST List 2.480

Sat 07 Sep 1991

Disc: Just In Case

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1. William J. Rapaport, Re: Announcement; Responses: in/on
2. , "Just in case"

Re: Just in case
The usage of this to mean "iff" is fairly common in philosophy; I've even
seen it in intro logic texts. I consider it an aberration. I've heard
it explained by one who used it as more or less short for "only if",
which is also often (incorrectly in my opinion) used where "iff" should be.
			William J. Rapaport
			Associate Professor of Computer Science
			Center for Cognitive Science
Dept. of Computer Science||internet: rapaportcs.buffalo.edu
SUNY Buffalo		 ||bitnet: rapaportsunybcs.bitnet
Buffalo, NY 14260	 ||uucp: {rutgers,uunet}!cs.buffalo.edu!rapaport
(716) 636-3193, 3180 ||fax: (716) 636-3464

	I am a logician. I studied with Tarski and Mates at Berkeley
and with Church at Princeton. Montague was a fellow student. I was a
colleague of Suppes. I met and known in my life Russell, Carnap,
Godel, Quine, Heyting, Beth, Mostowski, Kreisel, Kleene, Rosser,
Robinson, Dummmett, and many, many more logicians. My impression is
that none of these people would be surprised by the use of "just in
case" for "if, and only if". (Someone should ask Quine, since he is
very sensitive to language and terminology -- in many languages.)
	Here is my explanation about how this usuage came about.
First, in mathematics it is quite common to say things like:
	"The number x solves the problem just in these cases:
	 x < 3 or x > 7."
And there might just be a single case, say, x = 0, for some problems.
Here the word "case" means "particular instance," which I believe is a
well accepted sense. (And, of course, the word has other meanings as
well.)
	In more logical talk we say quite naturally, "It is the case
that "All me are mortal" is true." Even in everyday speech the
question, "Just what IS the case?", means clearly, "Come on, will you
finally tell me what is the real truth about the matter!"
	So, with the usual slide between use and mention (and without
bringing in quasiquotes), it does not seem difficult to understand how
people would say
	"P, just in case Q" for
	"It is the case that P is true exactly when (in the particular
	instance that) Q is true."
And this works out equivalent to "P if, and only if, Q".
	Is anyone convinced by this explanation?
						-- DANA SCOTT