 Yet another of Russell’s contributions is his defence of  neutral monism,  the view that the world consists of just one type of substance which is neither exclusively mental nor exclusively physical. Like idealism (the view that nothing exists but the mental) and physicalism (the view that nothing exists but the physical), neutral monism rejects dualism (the view that there exist distinct mental and physical substances). However, unlike both idealism and physicalism, neutral monism holds that this single existing substance may be viewed in some contexts as being mental and in others as being physical. As Russell puts it, 