Materialism is also a monism and differs from idealism only in denying to consciousness a direct intuition of all of its irreducible determinants. It is as if to say that side by side with the cogito there is another dark cogito, equally essential as a basis for experience but which affords no possible insight. (Or you might say that ide by side with the transcendental unity of apperception there is also a transcendental divergence of apperception, a dark matter of the mind.) But all of this only concerns what is defined as consciousness, and since any such definition is contingent on a view of experience there is nothing to stop you from redefining it, and redefining whatever is understood by intuition, logic, etc. to include this outside. You are never late enough to declare the terms fixed.