The technique of physics was developed under the influence of a belief in the metaphysical reality of "matter" which now no longer exists, and the new quantum mechanics has a different technique which dispenses with false metaphysics. The technique of psychology, to some extent, was developed under a belief in the metaphysical reality of the "mind." It seems possible that, when physics and psychology have both been completely freed from these lingering errors, they will both develop into one science dealing neither with mind nor with matter, but with events, which will not be labelled either "physical" or "mental."
Source: Religion and Science, 1935, chapt. 8
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