[Ralle]

> You say "can" be proven, are you saying they havent been
> proven yet? Because if they have, then you wouldn't use the
> word "can", you would use the word "have", no? Somebody
> else used the word "can" as well, that's why I'm wondering.

This is a valid question. For a theorem to be accepted as such
a proof would normally be required. Until the proof is presented
the "theorem" would usually be considered a conjecture.

However, in general we don't examine the proofs of all theorems
we encounter. Instead we take it for granted that a proof exists,
and that it is commonly accepted to be correct. It's just not
worth the bother to go through all proofs ourselves. And in many
instances, we are not even able to understand the proof. That is
why in practice it is enough that the theorem "can" be proved. But
like I said, that "can" is only a "can" for us, if you understand
what I mean.

Anyway, this is more a question of semantics. Maybe it's better to
simply use the word "have" like you suggest.