Comment by cauch

But you are the one both defending the argument and judging if they understood the argument.

If it is your argument, it means you believe in it, it means you think it is a good argument and not a bad argument. So maybe in fact they are right and they understood the argument correctly, but you are the one mistaken. How can you tell?

Let's, for the sake of discussion, imagine that your argument is bad. You believe it is good, but it is bad. It means that you don't yourself understand your own argument. How can you therefore judge if someone has understood the argument or not?

You were saying that you can see when they use "circular reasoning" and "rhetorical trick". That's exactly the first impression that everyone has when they defend a bad argument and someone points at the flaws in it.

I'm not mixing up "understanding" and "agreeing", I'm saying that you claim that you can tell if someone "understand", and I'm simply saying that it is not possible to tell if someone has understood if yourself you believe the argument is correct and they belief the argument is incorrect.