March 30, 2007

In which I pick up, and drop, a bad habit

`Just in case' does not mean `if and only if'. You bring along an umbrella just in case it rains; two sets are of the same cardinality just in the case that there is a bijection between them. What a difference a definite article makes!

Where did I pick up the habit of using `just in case' when I really meant `just in the case that'? Possibly from one Andrew M. Bailey. Except that I was doing it two years ago, quite a while before I met AB. More likely this nasty little meme has been circulating throughout the Anglophone philosophical community for quite some time, and both AB and I contracted it that way.


bradley said...

I bring an umbrella if and only if it rains. What I like better is, "My car has an air bag just in case I get in an accident." Ah! My car does have an air bag! (I owe that to Tom Crisp)

Andrew Bailey said...

I'm inclined to accept that "just in case" doesn't capture "if and only if" in natural English. It is the more elegant expression, however, and when speaking only to philosophers, confusion is unlikely.

Further, "just in the case that" fares no better at capturing the biconditional in natural language. "Just in the case that" sounds to me like "only in the case that," that is, "only if."

If I had been influenced more by PvI and less by Plantinga in my early philosophical years, I would have thought otherwise, I'm sure. Al is quite fond of the "just in case" locution while Peter has railed against it in many a footnote.

Noumena said...

If you follow the first link, the linguistic claims that `just in case' is an almost strictly American idiom. So confusion is only unlikely when speaking to American philosophers.