Pauline writes:I argue that it is impossible to ascribe ultimate authority to someone/something without said someone/something declaring itself the ultimate authority.
Then that should rule out your use of the Bible as an authority. When did you become an atheist?
Pauline writes:People of most commonly held worldviews, whether knowingly or unknowingly, declare one single thing/person to be the ultimate authority.
Not so.
Pauline writes:For instance, Christians declare God to the ultimate authority;
They may say that. But they are really declaring their favored theologians as the authority. If it were as easy as making God the authority, and settling issues by asking God and getting an answer, then we would not have so many disagreements between different Christian denominations and sects.
Pauline writes:Rationalists declare reason to be the ultimate authority
I don't think that's correct. I think they point to reason and evidence, not to reason alone.
I'm not sure why you don't see it, but pointing to reason and evidence as the ultimate authority is just a metaphoric way of speaking. People who say that are denying that there is an ultimate authority, and are saying that they will use their own reason and evidence rather than rely on any authority.
Pauline writes:Some but not all atheists declare science to be the ultimate authority.
Most would look to science as a source of evidence, but not as an authority. Science itself is full of people disagreeing with one another, trying to disprove the claims of one another. That does not look at all like what one might expect of an authority.
Pauline writes:No matter what the object may be, one cannot ascribe ultimate authority to it unless the object itself categorically declares itself 'I am the ultimate authority'.
If some entity declares itself the ultimate authority, you should run away as fast as you can. For, surely that entity is evil.
I still cannot understand why you think your OP is about circular reasoning.