Dualism is, in its broadest sense, founded on accepting that all is not one, that the distinctions we make between things are fundamentally real. Nondualism questions this. And nondualism as I see it it even questions the idea that the distinction between dualism and nondualism is very great. That is, it applies nondualistic thinking to the conversation about dualism and nondualism. Any philosophy that lacks such recursion isn't much of a philosophy to me.