Books I and II uphold the principles of the Atomic Theory as held by Epicurus (fl. 300 B.C.).
Book I states that the world consists of atoms and void. At line 694 is stated the important doctrine that the evidence of the senses alone is to be believed—sensus, unde omnia credita pendent, the senses on which rests all our belief.
Book II treats of the motions of atoms, including the curious doctrine of the swerve, which enables them to combine and makes freedom of will possible: then of their shapes and arrangement.
Book III shows the nature of mind (animus) and life (anima) to be material and therefore mortal. Therefore death is nothing to us:
Nil igitur mors est ad nos neque pertinet hilum,
Quandoquidem natura animi mortalis habetur.
Death therefore to us is nothing, concerns us not a jot,
Since the nature of the mind is proved to be mortal.—(M.)
Book IV gives Lucretius’ theory of vision and the nature of dreams and apparitions.
Book V explains the origin of the heavens, of the earth, of vegetable and animal life upon it, and the advance of human nature from a savage state to the arts and usages of civilisation.