As has been said by others: ideally, to the extent that I consider X likely without reference to A, A’s belief in X means I should consider A more credible, and to the extent that A is credible without reference to X, A’s belief in X means I should consider X more likely.
You’re right that in real life, humans skip the “without reference to” part and end up in loops, where we consider A more credible because A believes X, which we consider likely, and then we treat A’s belief in X as further reason to consider X likely. In other words, we double-count evidence, as various folks have said. Welcome to being humans rather than ideal reasoners.
When it’s possible to ignore other people’s testimony and credibility and just look at X without reference to anyone else’s opinion about it, that can be a helpful way of digging out of this particular tangle. When that isn’t possible, I try to ask myself why I trust a particular source, when I came to consider them credible, etc. … and if I don’t have a good answer, I try to ask myself whether I’d believe different things if I didn’t consider them credible.
I say “try” because I often fail at this. There are things I believe because someone told them to me once and I trusted them and I’ve long since forgotten the derivation.
We do what we can do, right?
Of course, there’s a million other sources of noise in our judgments, many of which drown this one out.
As has been said by others: ideally, to the extent that I consider X likely without reference to A, A’s belief in X means I should consider A more credible, and to the extent that A is credible without reference to X, A’s belief in X means I should consider X more likely.
You’re right that in real life, humans skip the “without reference to” part and end up in loops, where we consider A more credible because A believes X, which we consider likely, and then we treat A’s belief in X as further reason to consider X likely. In other words, we double-count evidence, as various folks have said. Welcome to being humans rather than ideal reasoners.
When it’s possible to ignore other people’s testimony and credibility and just look at X without reference to anyone else’s opinion about it, that can be a helpful way of digging out of this particular tangle. When that isn’t possible, I try to ask myself why I trust a particular source, when I came to consider them credible, etc. … and if I don’t have a good answer, I try to ask myself whether I’d believe different things if I didn’t consider them credible.
I say “try” because I often fail at this. There are things I believe because someone told them to me once and I trusted them and I’ve long since forgotten the derivation.
We do what we can do, right?
Of course, there’s a million other sources of noise in our judgments, many of which drown this one out.