 The central notion in the treatise is that of sensus (sense), which is directly connected to the principle of self-preservation. Every being displays a tendency toward the conservation of its own life and for this purpose is endowed, in varying proportions, with sense. This consists of the capacity to distinguish that which is positive and conducive to its life, and is consequently to be pursued and sought after, from that which is perceived as negative and destructive, and consequently to be shunned and avoided. Some entities such as celestial bodies and light possess a sense that is much sharper and purer than that of animals. Others such as minerals and metals have a sense that is more obtuse and obscure, due to the heaviness of matter. In animal organisms vital and cognitive functions depend on the spiritus. Hot, mobile and passive, it is identified with the organic soul. Rejecting the distinctions made by Galen between various abstract faculties, Campanella states that the spiritus is singular and has its seat in the brain, from where, flowing through very subtle nerve channels, it accomplishes its multiple functions, both vital and cognitive. By means of the sense organs, it comes into contact with external reality; all passions and cognition derive from the modifications that it undergoes. Every sensation is a form of “contact” on the part of the spiritus, that enters into a relation, via various sense organs, with the exhalations, motions and light coming from external objects. The sensations that the spiritus experiences are the source of all cognition: memory, imagination, reason and the intellect itself, which is nothing but weakened and distilled sense. There is no need to postulate different and specific faculties for such operations, since they are all functions of the same sentient soul, that is capable of preserving the modifications and impressions it receives and of reviving and re-using them when similar situations arise.