Final answer:
Physicalism in philosophy is the perspective that all existent things are physical and all knowledge is expressible in terms of physical objects and processes. It encompasses unity of science physicalism and causal physicalism, both of which reject dualism and idealism.
Step-by-step explanation:
In the field of philosophy, physicalism is a view that posits that all factual knowledge about the universe can ultimately be described through physical objects and phenomena. This doctrine maintains that everything that exists is physical in nature and that all causes, including those attributed to mental states or consciousness, are the result of physical processes. Physicalism can be considered an extension of materialism, with the belief that only physical substances exist and that mental processes are reducible to brain activity.
There are variations within physicalism, notably unity of science physicalism and causal physicalism. Unity of science physicalism suggests that all scientific knowledge can be unified under a common physicalist framework. On the other hand, causal physicalism focuses on the claim that every cause in nature is a physical cause. Both stances oppose the dualist view, which argues for the existence of both physical and non-physical substances, and idealism, which posits that reality is fundamentally mental or spiritual.