2009/5/4 René Uittenbogaard <[log in to unmask]>:

> We know that "but" is logically nothing more than "and" (both
> constituents are true).
> But is it symmetrical or asymmetrical?

It seems to me that "but" and "although"
are mirative forms of "and" -- that is, one asserts
that both propositions are true, and also expresses
surprise at the fact.   One of the propositions being
true makes it seem a priori unlikely that the other
would be true as well, but we find that it is, in fact,
the case.

P and Q: both P and Q are true.

P but Q: P is true, so one would suppose
that Q is false, but in fact it's true as well.

P although Q: P is true, which is pretty
surprising considering we know that Q
is also true.

The other posters in the thread have focused
on whether the preceding or following clause
is being emphasized by the "but"; I'm not sure
"emphasis" is the right word here.  It's a matter
of surprise or unexpectedness, one clause
being surprising or unexpected in light of
the other.

-- 
Jim Henry
http://www.pobox.com/~jimhenry/