I kind of figured you'd chime in here.

It is indeed a question of boundaries. And in one or more of the posts I previously linked to, I noted that the boundaries tend to be invisible ... notwithstanding that, as far as the three "classes" you've outlined, they "can" be well-defined.

For example, at the risk of being crude about it, classical physics would predict that any particle whatsoever should have characteristics A, B, C and D, and they all should be measurable. But in quantum physics we find that (under circumstances you're far more familiar with than I ever will be), if one measures A and C to a given degree of specificity, B and D become unmeasurable.

If one has a mind to debunk anyone else's belief; in short, IMO (and strictly IMO, though I feel quite strongly about it and do do my best to live this way) that's an appropriate "boundary" right there. As soon as one HAS such a mind, one's gone out of bounds.

P.