The idea in the philosophy of mind is that things that happen in the physical world have effects on the mind, but things that happen in the mind have no effect at all. In other words, the relationships between causes and effects only go from the physical to the mental.

Most people think of it as a type of dualism because it says that there are both physical and non-physical mental events. Still, because it is so different from substance dualism, it has sometimes been thought of in the past as a kind of monism.