This third volume of Rosmini's Psychology was written to clarify the circumstances in which the rational element of human nature has to act. Although essentially free - because every intellect has its seat in the infinite – the intelligence marvels at seeing itself surrounded and impeded in its upward flight by the material element on which it is so dependent. Moreover, the animal part of humanty is mysterious, highly difficult to investigate. and inexhaustible, especially in relationship to-instinct, the active part of animality.
Rosmini divides the animal activity of human nature into two great instincts, which he calls 'life instinct' and 'sensuous instinct', and deals briefly with both before passing to examine the struggles confronting the life instinct in its. Fight for survival, and the way in which it prompts the activity of the sensuous instinct.
Of particular interest is Rosmini's application of his work to the medical science if his time, with which he was throughly familiar. Many of his observations about method in medicine are still relevan today, and could usefully be employed in the development of holistic tendencies with which he would be wholly in sympathy. Several of his hypotheses, impossible to verify in his own day, have proved extraordinarily exact. 'Proprio-prerception'. for example- has great affinity with Rosmini's 'fundamental fueling'. Of particular interest is his affirmation that illness is an active, not a passive condition, and should be treated accordingly.