No man can exhaust by introspective analysis the hidden elements in his personality.
Subsequent psycho-physical investigations have all been in the spirit of his work; and although he consistently advocated the introspective method in psychological investigation, he was among the first to appreciate the help that may be given to it by animal and social and infant psychology.
One may say that this is another mark of the Prophet's want of mental training, and incapacity for introspective criticism.
This was possible in any complete sense only after the introspective movement represented by the middle ages had done its work, and the thought of the individual mind and will as possessed of relative independence had worked itself out into some degree of clearness.
The results of this introspective mysticism were collected by him in a series of fifty-four (originally forty-eight) treatises, arranged in six "Enneads," which constitute the most authoritative exposition of Neoplatonism.
Excluding from his enquiry " the physical consideration of the mind," he sought to make a faithful report, based on an introspective study of consciousness, as to how far a human understanding of the universe can reach.
Within the domain of consciousness introspective analysis is unable to discover those chains of necessary sequences which it is the province of science to investigate in the physical world.