A pretty good test is to ask each side to summarize the other side's position in a way the other side would endorse. If one side succeeds, and the other fails,

A pretty good test is to ask each side to summarize the other side's position in a way the other side would endorse. If one side succeeds, and the other fails, that reveals who understands both positions, and who doesn't. Of course they can still make excuses, such as saying that they don't understand the other guy's position because he didn't explain it clearly. And they can say they asked questions about it to try to understand, but he still didn't answer well. That could even be true. But it usually isn't.