 The structure of the treatise is indebted to the traditional approach of faculty psychology, in which the soul is said to be composed of a number of different faculties or powers, each directed toward a different object and responsible for a distinct operation. The first book covers the functions of the vegetative soul (nutrition, growth and reproduction), of the sensitive soul (the five external senses), and of the cogitative soul (the internal senses, i.e., a variety of cognitive faculties, including imagination, fantasy and the estimative power, which are located in the three ventricles of the brain, and whose acts follows from the acts of the external senses). The second book deals with the functions of the rational soul and its three faculties (mind, will, and memory), as well as with topics stemming from Aristotle’s Parva naturalia, such as sleep, dreams, and longevity. The third and final book explores the emotions, which Vives, rejecting the Stoic view, regards as natural responses to the way things appear to us and as essential constituents of human life.