But what, actually, is the psyche? Materialistic prejudice explains it as a mere epiphenomenal by-product of organic processes in the brain.
Any psychic disturbance must therefore be an organic or physical disorder which is undiscoverable only because of the inadequacy of our present methods of diagnosis.
The undeniable connection between psyche and brain gives this point of view a certain weight, but not enough to make it an unshakable truth.
We do not know whether there is a real disturbance of the organic processes in the brain in a case of neurosis, and if there are disorders of an endocrine nature it is impossible to say whether they might not be effects rather than causes. Carl Jung, Psychology and Religion, Page 11., Paragraph 14.