Non-reductive materialism (or materialism) is considered a from of monism, in the sense that ontologically everything is considered to be made of physical substances. It is non-reductive only in that it holds that some properties can never be explained in terms of lower level physical properties, even if they pretain to material objects. A non reductive materialist holds for example that mental properties, even though themselves physical, can never be explained in terms of neural states. Another example of non-reductive materialism would be our inability to explain biological causes in purely physical and chemical terms. I've seen this position also described as naturalism (in the context of John Searle's theory of mind).
More recently, there was this paper on the undecidability of certain quantum hamiltonians, challenging the reducibility of the macroscopic to the microscopic.
My question is: does this really count as monism? Isn't it for all practical purposes dualism?
I've seen Kant described as a dualist because of his noumenon/phenomenon dichotomy. But then based on the same logic, isn't dividing the world to ontologically identical, yet logically non-reducible, and therefore epistemically independent realms, amount to a form of dualism?