This wrath was supposed to be displayed by the misfortunes inflicted in this life and by the everlasting tortures that were the lot of the guilty in a future state or, where these feelings were not strongly developed, from a vague dread of gloom and misery after death.

To do this, Epicurus invoked the atomism of Democritus to demonstrate that the material universe was formed not by a Supreme Being but by the mixing of elemental particles which had existed from all eternity, governed by certain simple laws.

He argued that the deities (whose existence he did not deny) lived forever in the enjoyment of absolute peace—strangers to all the passions, desires and fears, which affect humans—and are totally indifferent to the world and its inhabitants, unmoved alike by their virtues and their crimes.

He argues against fear of such deities by demonstrating, through observations and arguments, that the operations of the world can be accounted for in terms of natural phenomena, which are the result of regular but purposeless motions and interactions of tiny atoms in empty space.

The first three books provide a fundamental account of being and nothingness, matter and space, the atoms and their movement, the infinity of the universe both as regards time and space, the regularity of reproduction (no prodigies, everything in its proper habitat), the nature of mind (animus, directing thought) and spirit (anima, sentience) as material bodily entities, and their mortality, since, according to Lucretius, they and their functions (consciousness, pain) end with the bodies that contain them and with which they are interwoven.

The last three books give an atomic and materialist explanation of phenomena preoccupying human reflection, such as vision and the senses, sex and reproduction, natural forces and agriculture, the heavens, and disease.

[4][5] By recalling the opening to poems by Homer, Ennius, and Hesiod (all of which begin with an invocation to the Muses), the proem to De rerum natura conforms to epic convention.

The shape of these atoms, their properties, their movements, the laws under which they enter into combination and assume forms and qualities appreciable by the senses, with other preliminary matters on their nature and affections, together with a refutation of objections and opposing hypotheses, occupy the first two books.

[3] The fourth book is devoted to the theory of the senses, sight, hearing, taste, smell, of sleep and of dreams, ending with a disquisition upon love and sex.

[8] This book addresses the origin of the world and of all things therein, the movements of the heavenly bodies, the changing of the seasons, day and night, the rise and progress of humankind, society, political institutions, and the invention of the various arts and sciences which embellish and ennoble life.

[3] The sixth book contains an explanation of some of the most striking natural appearances, especially thunder, lightning, hail, rain, snow, ice, cold, heat, wind, earthquakes, volcanoes, springs and localities noxious to animal life, which leads to a discourse upon diseases.

[10] The German classicists Ivo Bruns and Samuel Brandt set forth an alternative theory that Lucretius did at first write the poem with Memmius in mind, but that his enthusiasm for his patron cooled over time.

[13] Memmius was also a tribune in 66, praetor in 58, governor of Bithynia in 57, and was a candidate for the consulship in 54 but was disqualified for bribery, and Stearns suggests that the warm relationship between patron and client may have cooled (sed tua me virtus tamen et sperata voluptas / suavis amicitiae quemvis efferre laborem, "But still your merit, and as I hope, the joy / Of our sweet friendship, urge me to any toil").

[13][14] There is a certain irony to the poem, namely that while Lucretius extols the virtue of the Epicurean school of thought, Epicurus himself had advised his acolytes from penning poetry because he believed it to make that which was simple overly complicated.

[19] For instance, the poem concludes rather abruptly while detailing the Plague of Athens, there are redundant passages throughout (e.g., 1.820–821 and 2.1015–1016) alongside other aesthetic "loose ends", and at 5.155 Lucretius mentions that he will spend a great deal of time discussing the nature of the gods, which never comes to pass.

[5] To further alleviate the fear of non-existence, Lucretius makes use of the symmetry argument: he argues that the eternal oblivion awaiting all humans after death is exactly the same as the infinite nothingness that preceded our birth.

[31][32] Thus, he began his discussion by claiming that he would explain by what forces nature steers the courses of the Sun and the journeyings of the Moon, so that we shall not suppose that they run their yearly races between heaven and earth of their own free will [i.e., are gods themselves] or that they are rolled round in furtherance of some divine plan....[33]However, when he set out to put this plan into practice, he limited himself to showing how one, or several different, naturalistic accounts could explain certain natural phenomena.

If the latter is true, Lucretius, notes, this is because: "either swift currents of ether whirl round and round and roll their fires at large across the nocturnal regions of the sky"; "an external current of air from some other quarter may whirl them along in their course"; or "they may swim of their own accord, each responsive to the call of its own food, and feed their fiery bodies in the broad pastures of the sky".

[36] Drawing on these, and other passages, William Stahl considered that "The anomalous and derivative character of the scientific portions of Lucretius' poem makes it reasonable to conclude that his significance should be judged as a poet, not as a scientist.

Lucretius attempts to allow for free will in his physicalistic universe by postulating an indeterministic tendency for atoms to veer randomly (Latin: clinamen, literally "the turning aside of a thing", but often translated as "the swerve").

[41] Martin Ferguson Smith notes that Cicero's close friend, Titus Pomponius Atticus, was an Epicurean publisher, and it is possible his slaves made the very first copies of De rerum natura.

It has been suggested that Dante (1265–1321) might have read Lucretius's poem, as a few verses of his Divine Comedy exhibit a great affinity with De rerum natura, but there is no conclusive evidence for this hypothesis.

Additionally, although only published in 1996, Lucy Hutchinson's translation of De rerum natura was in all likelihood the first in English and was most likely completed some time in the late 1640s or 1650s, though it remained unpublished in manuscript.

[63][64] It is also believed that G. Julius Caesar alludes to Lucretius' work variously in his Gallic Wars,[65] just as the Roman poet Virgil referenced Lucretius and his work in the second book of his Georgics when he wrote: "Happy is he who has discovered the causes of things and has cast beneath his feet all fears, unavoidable fate, and the din of the devouring Underworld" (felix qui potuit rerum cognoscere causas/atque metus omnis et inexorabile fatum/subiecit pedibus strepitumque Acherontis avari).

[5][66][67] According to David Sedley of the Stanford Encyclopedia of Philosophy, "With these admiring words, Virgil neatly encapsulates four dominant themes of the poem—universal causal explanation, leading to elimination of the threats the world seems to pose, a vindication of free will, and disproof of the soul's survival after death.

[90] While he argued that Lucretius's criticism of Roman religion were "sound attacks on paganism and superstition", Lactantius claimed that they were futile against the "True Faith" of Christianity.

The one major exception to this was Isidore of Seville, who at the start of the 7th century produced a work on astronomy and natural history dedicated to the Visigothic king Sisebut that was entitled De natura rerum.

[99] In 2011, the historian and literary scholar Stephen Greenblatt wrote a popular history book about the poem, entitled The Swerve: How the World Became Modern.

In the work, Greenblatt argues that Poggio Bracciolini's discovery of De rerum natura reintroduced important ideas that sparked the modern age.