Neutral monism is an umbrella term for a class of metaphysical theories in the philosophy of mind, concerning the relation of mind to matter. These theories take the fundamental nature of reality to be neither mental nor physical; in other words it is "neutral".[1]
Neutral monism has gained prominence as a potential solution to theoretical issues within the philosophy of mind, specifically the mind–body problem and the hard problem of consciousness. The mind–body problem is the problem of explaining how mind relates to matter. The hard problem is a related philosophical problem targeted at physicalist theories of mind specifically: the problem arises because it is not obvious how a purely physical universe could give rise to conscious experience. This is because physical explanations are mechanistic: that is, they explain phenomena by appealing to underlying functions and structures. And, though explanations of this sort seem to work well for a wide variety of phenomena, conscious experience seems uniquely resistant to functional explanations. As the philosopher David Chalmers has put it: "even when we have explained the performance of all the cognitive and behavioral functions in the vicinity of experience - perceptual discrimination, categorization, internal access, verbal report - there may still remain a further unanswered question: Why is the performance of these functions accompanied by experience?".[2]
With this, there has been growing demand for alternative ontologies (such as neutral monism) that may provide explanatory frameworks more suitable for explaining the existence of consciousness. It has been accepted by several prominent English-speaking philosophers, such as William James and Bertrand Russell.