T4.3 3 of 6

We have just seen certain cases in which "unless" is properly translated as the wedge. But we have also seen why we associate an exclusivity with these expressions: something other than the connective expresses "not both".

Much the same can be said for "or". Think about our case about the soup or salad. What's exclusive here is not the meaning of "or". But also it's not an impossibility of having both soup and salad. Rather, there is a practical exclusivity involved:

Suppose, that our waiter knows that both soup and salad are included with a certain meal. It would then be unreasonable of the waiter to say "you will get one or the other". Still, it would not be false to say one could have one or the other: If that were false, then it would be true that one could have neither!

Instead, the problem with saying "one will have either have soup or salad" is that this is holding back; the waiter should say more, that you can have both. By saying less than this, by withholding information, he is misleading us. This is not to tell a falsehood, but nonetheless is breaking a rule of good conversation: he's not being informative as he should.

Of course there are lots of ways to mislead without saying something false. Remember that mistakes need not be falsehoods. One can truly utter things which are insulting, embarrassing, uninteresting, clumsy, hard to understand, profane in a polite context, etc. All are conversational mistakes. So, we should not conclude that the waiter's statement is false when it is only misleading. But it's still a gross mistake on his part. Stiff him for the failure!

So, the conversational principle of informativeness implies that when we think of the conditions of use for "or", one should typically not say "P or Q" when one knows that both P and Q are true and so could say more, could reasonably say "P and Q".

This, finally(!), gives us our bottom line.

There are reasons to think that phrases containing words like "or" and "unless" involve a kind of exclusivity. But this does not imply that the English word ("or" or "unless") means anything about the exclusivity. Instead, exclusivity is a matter of other aspects of the expression. (E.g., the meaning of the disjuncts T,E or the principle of informativeness.)

Either way, we can translate "or" or "unless" as a wedge.

 

Next...