From my shortform:
If you know someone is rational, honest, and well-read, then you can learn a good bit from the simple fact that they disagree with you.
If you aren’t sure someone is rational and honest, their disagreement tells you little.
If you know someone considers you to be rational and honest, the fact that they still disagree with you after hearing what you have to say, tells you something.
But if you don’t know that they consider you to be rational and honest, their disagreement tells you nothing.
It’s valuable to strive for common knowledge of you and your partners’ rationality and honesty, to make the most of your disagreements.
This is a restatement of the ideas behind Aumann’s Agreement Theorem. On Less Wrong, one can often assume that a writer or commentor is interested in rationality, but that doesn’t mean that the writer can be assumed to actually be rational.
How can we help build common knowledge of people’s rationality and honesty?