What about the fact that no factual claim can be derived from logic?
If so, the assumption that everything can be doubted
can itself also be doubted.
It is not a logical assumption at all, but an epistemological one.

I didn't understand.

The assumption that one can cast doubt on everything that exists is not a logical claim, but an epistemic one.
Whether that thing exists or not, casting doubt does not change the reality of things in the world.

Likewise, casting doubt on arguments is also not a logical claim, because if the argument is valid then it is valid, and if not then not—unless you are casting doubt on logic itself.

What remains is to cast doubt on the assumptions themselves about the state of affairs in the world, but as I mentioned, most assumptions are epistemic. So the method of casting doubt can itself also be doubted. That is, the assumption that everything can be doubted is itself doubtful and saws off the branch it sits on.

—
Does the Rabbi agree?

Absolutely not.

Why? Which assumption?

I explained my claim and I didn't see any argument against it from you.

First, I'm not the original questioner.
Second, in your answer to him you wrote that one cannot cast doubt on doubting itself, because the ability to cast doubt on anything is a logical claim, and as such it is not to be doubted. Doubts are cast on factual claims.

But as I told you, that ability may be logical, but the assumption regarding its correctness is already epistemic.
I don't see how what you wrote leads you to completely disagree with what I said.

It is not clear that doubt is cast only on factual claims. In any case, that wasn't my assumption. My claim is that one should not cast doubt on logical claims, like the law of non-contradiction or De Morgan's laws. But for the sake of the discussion I will adopt your formulation, that doubt is cast only on factual claims.
The claim that one can cast doubt on every claim (let us say, factual), is itself not a factual claim. It only means that whatever is not logically necessary is not certain. That claim itself is not factual but logical, and therefore there is room to say that one should not cast doubt on it. That certainly does not contradict the claim that one can cast doubt on every factual claim.

Of course one can cast doubt on every factual claim; the question is whether that doubting has epistemic significance. Here it seems that you accept what I said.

I don't think everything is doubtful. At one point I did think that, but really I wanted to clarify the rule. A more precise wording would have been: why is there "no doubt about the ability to cast doubt"? So my first question is: why can't one cast doubt on a logical claim, while one can cast doubt on a factual claim? Is that just some arbitrary rule that somebody made up, or is there some logic behind the distinction?
And question 2: once two people, for the sake of discussion, accept the laws of logic, then you get a situation where if this, then that, and if that, then this. But the laws of logic themselves are arbitrary, and there is nothing absolute about their being correct. In my opinion that is really no different from blind faith. The absoluteness exists only in the logical conclusions after we have accepted the rules of reasoning. And question 3: when people say in debates that in this situation the burden of proof is on you and in that situation it is on me, is that also just an arbitrary rule that somebody came up with?

Is it possible that by mistake I answered question 1 myself with question 2? In any case I'd be happy to get an answer to 2 and 3, and to 1 as well if needed.

I don't see where this discussion is going. I explained what I had to explain. I'm done.