There
may not be proof that one set of principles is the only true or
binding set of principles. But maybe there is something else almost as
good.
Ayesha already said that principles may not be the sort of thing that
is true or false, but that they can be adopted for various reasons.
One set of principles may be conducive to human happiness. Another may
prevent suffering.
My point is that in the absence of proof we may still have good
reasons to adopt one set of principles rather than another.