In philosophy, physicalism is the metaphysical thesis that "everything is physical", that there is "nothing over and above" the physical, or that everything supervenes on the physical. Physicalism is a form of ontological monism—a "one substance" view of the nature of reality as opposed to a "two-substance" (dualism) or "many-substance" (pluralism) view. Both the definition of "physical" and the meaning of physicalism have been debated.
Physicalism is closely related to materialism, and has evolved from materialism with advancements in the physical sciences in explaining observed phenomena. The terms "physicalism" and "materialism" are often used interchangeably, but can be distinguished based on their philosophical implications. Physicalism encompasses matter, but also energy, physical laws, space, time, structure, physical processes, information, state, and forces, among other things, as described by physics and other sciences, as part of the physical in a monistic sense. From a physicalist perspective, even abstract concepts such as mathematics, morality, consciousness, intentionality, and meaning are considered physical entities, although they may consist of a large ontological object and a causally complex structure.
According to a 2009 survey, physicalism is the majority view among philosophers, but there remains significant opposition to physicalism. Neuroplasticity has been used as an argument in support of a non-physicalist view. The philosophical zombie argument is another attempt to challenge physicalism.
Outside of philosophy, physicalism can also refer to the preference or viewpoint that physics should be considered the best and only way to render truth about the world or reality.
The word "physicalism" was introduced into philosophy in the 1930s by Otto Neurath and Rudolf Carnap.
The use of "physical" in physicalism is a philosophical concept and can be distinguished from alternative definitions found in the literature (e.g., Karl Popper defined a physical proposition as one that can at least in theory be denied by observation).