Quod simul atque hominem leti secura quies est
Indepta atque animi natura animaeque recessit,
Nil ibi libatum de toto corpore cernas
Ad speciem, nil ad pondus: mors omnia praestat
Vitalem praeter sensum calidumque vaporem[10].
Four distinct elements enter into the composition of the soul—heat, wind, calm air, and a finer essence 'quasi anima animai.' The variety of disposition in men and animals depends on the proportion in which these elements are mixed.
The soul is the guardian of the body, inseparably united with it, as the odour is with frankincense; nor can the soul be disconnected from the body without its own destruction. This intimate union of soul and body is proved by many facts. They are born, they grow, and they decay together. The mind is liable to disease, like the body. Its affections are often dependent on bodily conditions. The difficulties of imagining the state of the soul as existing independently of the body are next urged; and the book concludes with a long passage of sustained elevation of feeling, in which the folly and the weakness of fearing death are passionately insisted upon.
The fourth book, which treats of the images which all objects cast off from themselves, and, in connexion with that subject, of the senses generally, and of the passion of love, is intimately connected with the preceding book. If there is no life after death, what is the origin of the universal belief in the existence of the souls of the departed? Images cast off from the surface of bodies, and borne incessantly through space without force or feeling, appearing to the living sometimes in sleep and sometimes in waking visions, have suggested the belief in the ghosts of the dead, and in many of the portents of ancient mythology. The rapid formation and motion of these images and their great number are explained by various analogies. Some apparent deceptions of the senses are next mentioned and explained. These deceptions are shown to be not in the senses, but in our minds not rightly interpreting their intimations. There is no error in the action of the senses. They are our 'prima fides'—the foundation of all knowledge and of all conduct—
Non modo enim ratio ruat omnis, vita quoque ipsa
Concidat extemplo, nisi credere sensibus ausis[11].