Readers have always acknowledged the comparatively clear macrostructure of De rerum natura 3. It begins with a prooemium in which is described the terrifying impact which the fear of death has on human lives, as well as the fact that Epicurus has provided a cure against this fear, namely his physical doctrines (1–93). Particular attention is paid to fears of an afterlife in which we have to suffer pain and grief in the underworld; cf., for instance, the programmatic lines 3.37–40 (translation by Ferguson Smith, which will be used throughout):
This prooemium is followed by a long passage (94–829) in which Lucretius explains the basics of Epicurean psychology and tries to show that the soul is (like the body) material and hence mortal; this last point is driven home with particular force in II. 417–829 where Lucretius lists twenty-five proofs for the mortality of the soul.