The mind-body problem arises because mental phenomena arguably differ, qualitatively or substantially, from the physical body on which they apparently depend. There are a few major theories on the resolution of the problem. Dualism is the theory that the mind and body are two distinct substances, and monism is the theory that they are, in reality, just one substance. Monist materialists/physicalists take the view that they are both matter, and monist idealists take the view that they are both in the mind. The absence of an empirically identifiable meeting point between the non-physical mind and its physical extension has proven problematic to dualism and many modern philosophers maintain that the mind is not something separate from the body.