This proposition however contradicts supervenience physicalism, which asserts a denial of dualism. Unlike token physicalism, type physicalism entails supervenience physicalism. Philip Goff similarly describes panpsychism as an alternative to both physicalism and substance dualism. Both substance and property dualism are opposed to reductive physicalism. Token physicalism is not however equivalent to supervenience physicalism. Strawson has argued that what he calls "realistic physicalism" entails panpsychism. Recently, epiphenomenalism has gained popularity with those struggling to reconcile non-reductive physicalism and mental causation. Donald Davidson's anomalous monism is an attempt to formulate such a physicalism. The strong version of emergentism is incompatible with physicalism. A further problem for supervenience-based formulations of physicalism is the so-called "necessary beings problem". Most metaphysical naturalists have adopted some form of materialism or physicalism. Likewise, some philosophers feel that these dichotomies necessitate a switch from materialism to physicalism. However, the weak version of emergentism is compatible with physicalism. Others use the terms "materialism" and "physicalism" interchangeably. One version of reductive physicalism is type physicalism or mind-body identity theory.