Taffer said:
Eleatic Stranger, that can only be said for our universe, because it is the only universe we have ever experienced. And I am not talking about 1+1=2 in the 'language' sense. Of course 1+1=2, beacuse 2, by definition, is 1+1. What I am saying is that we cannot say it is impossible to have a universe where one apple with another apple gives three such apples, because we have never experienced every possible universe.
Ah, I think I see where we misunderstood one another.
When we say "1 + 1 = 2", that to me is maths.
When we say "One apple plus another apple is two apples", we then (to my mind) start to move in to the
application of mathematics to the real world, and empirical sciences. This was my idea of maths being a tool to understand science and not a science in and of itself.
The thing is, though, that if we find that the maths doesn't reflect the real-world situation, we can invent a new system of maths. For example, in a scalar sum, one kilometre plus one kilometre equals two kilometres. But in a vector sum, one kilometre north plus one kilometre west equals sqrt(2) kilometres north-west. The reason I think maths doesn't have a "real" existence (to address Interesting Ian) is that we can do this -- we can start with new axioms and construct different mathematical systems which are perfectly consistent in and of themselves, and which may (or may not) have a relationship with the real world.
Now, to be honest, I can't conceive of a universe where one apple plus one apple equals three apples, but I'm prepared to accept that as a lack of imagination on my part. I'm similarly unable to conceive, say, 11 dimensions, but that doesn't mean it's not a useful or possible concept. I'm sure it wouldn't be beyond mathematicians to come up with systems to deal with addition of apples in that universe (though it's certainly beyond me

)
But, as Eleatic Stranger points out, "1 +1 = 2" -- given our definitions of 1, 2, + and = and the axioms governing them -- is true for all possible universes, unless
we change the axioms. If it turned out that one apple plus one apple gave three apples, we could change the axioms such that "1 + 1 = 3" (though I don't know how we'd accomplish that), but that wouldn't invalidate the old axioms and the statement "1 + 1 = 2 under the old axioms" -- it would just be a different system of maths.
I'm starting to be of the opinion that it's neither science nor philosophy and that it deserves a nice little box all of its own
