Monism

Monism is the philosophical view that only one sort of stuff in the universe exists ultimately (see reduction). Monism is to be distinguished from dualism, which holds that ultimately there are two kinds of stuff.

So there are two kinds of monism, namely, physicalism and PhenomenalIsm?; the former holds that the mental can be reduced to the physical, and the latter holds the converse.

There is, in fact, another kind of monism, neutral monism, which holds that both the mental and the physical can be reduced to some sort of "neutral stuff."