Would a materialist and reductionist have to reject the phenomena/noumena

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Would a materialist and reductionist have to reject the phenomena/noumena distinction? I saw a clip of a debate between Christopher Hitchens and Douglas Wilson in which Hitchens seems to claim that one could reject the supernatural without rejecting the noumenal. To truly believe in a hidden "thing in itself" wouldn't you have to take a leap of faith, so to speak? You would have to assert that we should believe in something unprovable, which would seem to be the antithesis of Hitchens' normal position. Thanks!