[FOM] Why inclusive disjunction?

Richard Zach rzach at ucalgary.ca
Thu Jan 11 19:31:31 EST 2007

    May I recommend

    Robert B. Barrett; Alfred J. Stenner, The myth of the exclusive
    `or'.*  */Mind/ 80 (1971) 116-121.

        Stable URL:

as an interesting (and, I think, influential) argument for why there are 
no *truth functional* uses of "or" as exclusive disjunctions in 
English?  If they are right that "or" is never correctly formalized by 
exclusive disjunction, then the tendency to read/formalize "or" as 
inclusive disjunction is perhaps best explained the same way the 
tendency of reading "if then" as the material conditional is: it's the 
best you can do if you only have truth functions.  (Just to make this 
clear: they don't say that "or" is never used in an exclusive sense, 
only that these aren't truth-functional uses.)

See also


which summarizes Jennings' /The Genealogy of Disjunction/ (OUP, 1994), 
which contains lots of historical detail concerning inclusive and 
exclusive or, and what he calls the "myth of vel and aut"--that Latin 
"vel" corresponds to inclusive disjunction and "aut" to exclusive 

I also wanted to point out that inclusive disjunction together with 
negation is truth functionally complete, whereas exclusive disjunction 
and negation aren't.  This has nothing to do with why logicians tend to 
interpret "or" as inclusive disjunction, but it may have something to 
with why mathematical logicians prefer inclusive disjunction as a 
primitive connective.


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