Since we know nothing about the intrinsic quality of physical events except when these are mental events that we directly experience, we cannot say either that the physical world outside our heads is different from the mental world or that it is not. The supposed problem of the relations of mind and matter arises only through mistakenly treating both as "things" and not as groups of events. With the theory that I have been suggesting, the whole problem vanishes.
Source: Bertrand Russell : Mind and Matter (1950?)
More info.:https://russell-j.com/beginner/19501110_Mind-Matter210.HTM