The chief propositions in regard to the human mind viewed as a substantial principle which Catholic philosophers claim to establish by the light of reason are, its abiding unity, its individuality, its freedom, its simplicity, and its spirituality (see CONSCIOUSNESS; INDIVIDUALITY; INTELLECT; SOUL).
He identifies mens with the human soul viewed as intellectual and abstracting from lower organic faculties.
Angels, or pure spirits, may thus be called minds (De Veritate, X, a. For Descartes the human soul is simply mens, res cogitans , mind.
Consequently metaphysical or rational psychology logically follows empirical or phenomenal psychology.
The careful observation, description, and analysis of the activities of the mind lead up to our philosophical conclusions as to the inner nature of the subject and the source of those activities.
Mind adequately conceived must thus be held to include the subject or agent along with states or activities, and it should be the business of a complete science of mind to investigate both.
All our rational knowledge of the nature of the mind must be derived from the study of its operations.If we define the soul as the principle within me, by which I feel, think, will, and by which my body is animated, we may provide a definition of mind of fairly wide acceptance by merely omitting the last clause.That is, in this usage mind designates the soul as the source of conscious life, feeling, thought, and volition, abstraction being made from the vegetative functions.In favour of the doctrine of unconscious mental processes have been urged the fact that many of our ordinary sensations arise out of an aggregate of impressions individually too faint to be separately perceivable, the fact that attention may reveal to us experiences previously unnoticed, the fact that unobserved trains of thought may result in sudden reminiscences, and that in abnormal mental conditions hypnotized, somnambulistic, and hysterical patients often accomplish difficult intellectual feats whilst remaining utterly unaware of the rational intermediate steps leading up to the final results.On the other side it is urged that most of those phenomena can be accounted for by merely subconscious processes which escape attention and are forgotten; or, at all events, by unconscious cerebration, the working out of purely physical nervous processes without any concomitant mental state till the final cerebral situation is reached, when the corresponding mental act is evoked.Aristotle tells us that Anaxagoras, as compared with other early Greek philosophers, appeared like one sober among drunken men in that he introduced nous , mind, as efficient cause of the general order in the universe.