Consciousness dualists argue that materialism is false because of the conceivability of zombie which has no consciousness. The argument from conceivability applies to consciousness asymmetrically with $Water=H_2O$ whose identity was already established. However I think that argument is unsound because asymmetric application Is implausible. First, the metaphysical sap between water and $H_2O$ must be filled not by conceptual analysis, but by empirical methods: the neuroscientific developments will fill the metaphysical gap of consciousness. Second, consciousness dualists said it is illusion when we seem to conceive of $H_2O$ without water, but it is not illusion when we conceive the tumble with no consciousness. I argue it is also illusion in the case of latter. So two cases must be concerned equally.