The dualist claims that there are two fundamental things in the universe. In this paper, I focus on the dualist theory in the philosophy of mind, which is also called mind-body dualism. This theory suggests that the mind and the body are in fact different things in some respect. In the substantial respect, it is called substance dualism. In the property respect, it is property dualism. In the conceptual respect, it is conceptual dualism. In this paper, I argue that no matter what kind of dualism it is, if we hold that (1) the mind and the body have causal relationship or (2) the mind is generated from the body, we will not be able to stand well on the dualist ground and will slip into monism.