Materialists say sensations and other kinds of mental states are physical events. Today, most materialists are neural materialists. They think mental states are neural events or material properties of neural events.

Orthodox neural materialists think mental states are neural events or orthodox material properties of neutral events. Orthodox material properties are defining properties of the physical. A defining property of the physical is a type of property that provides a necessary condition for something's being correctly termed ‘physical’ (a conjunction of all defining properties provides a sufficient condition.) Defining properties of the physical include spatial and temporal properties and causal propensities and sensitivities. A particle is an electron, for instance, by having a particular set of spatiotemporal properties and causal sensitivities and powers.