In this way it is like mathematics. Mathematical theorems are not derived from definitions as Kant saw, as opposed to Hume. The Talmud is the same in this respect.
But because it is a priori does not make it immune from criticism. Though in general we know that you can't derive an "ought" from an "is" and the whole Talmud is only about "ought;"--still it is not a logical fallacy to determine how well your logical deductions have been based on an "is."
It looks to me that Conservative Judaism is a much closer approximation to the Torah and Talmud than any other branch.
[I asked Kelley Ross about objective morality. I put his answer on my other blog. I was wondering about the proof of Michael Huemer. [together with this ] [and this]He still thought that Plato's proof was more simple and straightforward.] John Searle has a refutation of relativism here
Dr Kelley Ross's answer is worded in a way that might be not understood. What he means in his essay on moral relativism is it is logically incoherent since it can not deny its opposite. That is is has no meaning but is just a play on words.