[FOM] Disjunction: in or ex?

Charles Silver silver_1 at mindspring.com
Thu Jan 11 18:51:09 EST 2007

On Jan 11, 2007, at 4:03 PM, Martin Davis wrote:

> Legal: In contracts in the US, I have seen "and/or" used to indicate
> inclusive disjunction.

	Oddly, the slash ('/') "could be" inclusive or exclusive.  If  
inclusive, then when the "or" is inclusive, the "and" doesn't add  
anything, it just clarifies.  However when the '/' is exclusive, then  
still assuming that the "or" is inclusive, either the "and" holds or  
the (inclusive) "or" holds, but not both, which is contradictory  
(when the "and" case holds).

	But take the '/' to be inclusive and the "or" exclusive.  Then,  
either or both the "and" holds or the (exclusive) "or" holds.  But  
they cannot hold together.  Another contradiction. But take the '/'  
to be exclusive and the "or" exclusive too.  Then, either the "and"  
holds or the (exclusive) "or" holds, but not both, meaning exactly  
one of "and" and "exactly one" hold, which seems okay.

	So, it looks like (supposing I haven't made a mistake) the '/' can  
be inclusive and the "or" inclusive as well, and the '/' can be  
exclusive and the "or" exclusive as well.

	To me, it seems clear that the '/' is meant inclusively.  Thus, the  
"or" must be inclusive as well.  This is backed up by the dictionary  
meaning of "and/or".
	*Conclusion* (from Martin's legal point): The "or" is definitely  

(But, since the exclusive '/' and the "exclusive or" are consistent,  
maybe someone might wish to argue for that pair.)

	(Hope I haven't screwed up this argument.)

Charlie Silver

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