One might say, though this would be putting it too crudely, that physics is concerned with causal relations outside the brain and psychology with causal relations inside the brain - excluding, in the latter case, those which are discovered by the external observation of the physiologist inspecting the brain. The data for both physics and psychology are events which, in some sense, happen in the brain. They have a chain of external causes, which are investigated by physics, and a chain of internal effects - memories, habits, etc. - which are investigated by psychology. But there is no evidence of any fundamental difference between the constituents of the physical and the psychological world.
Source: Religion and Science, 1935, by Bertrand Russell
More info.:
https://russell-j.com/beginner/RS1935_05-180.HTM
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