I'm slightly at a loss - I can't now see how you can't see that your justification of the principle is circular.

I'm equally at a loss as to why you think I believe it isn't. I know it's circular. I just don't see how that negates me treating it as an experiential axiom.

I say it's based on experience. It doesn't seem to me that that says anything either way about whether or not the justification for it's circular.

And I still can't see what you base your use of it on, if not your experience that it works.