Mental/Physical Relations
Our ideas of what external nature is will always be subject to change as we gain new experimental knowledge, but there is a part of our attitude to nature which should not be subject to future change, namely that part which rests on the permanent basis of the character of our minds.
“(1) Psychology is supposed to be the study of mind, but since no one knows what is meant by mind, it is impossible to define psychology. No operational criteria have been discovered by which so-called mental and physical events can be distinguished. The nature of all events is ontologically the same.”