Lucretius begins by invoking the name of Venus as a creative force, appealing to Memmius (to whom the work is addressed), and then praising his master Epicurus. (Scholars have noted the seeming inconsistency in Lucretius' invoking Venus at the beginning of a work that disclaims the gods' involvement with human life. The solution most commonly offered is that such a invocation was standard in the literature of the time, and that by keeping to the standard Lucretius hoped to win the trust and continued attention of readers.) Lucretius states that religion teaches fear, while science teaches fact. He recounts the story of Agamemnon, who was willing to sacrifice his daughter Iphigenia for the good will of the gods. This is not piety, Lucretius says, but rather wickedness demanded by religion.
Next, Lucretius sets about describing atoms as the building blocks of every object and living thing in the world. Nothing comes from nothing, and no object can ever be reduced to nothing. Although atoms cannot be seen, their presence can be felt in the wind, evaporation and humidity, and sensory experience. The entire world is composed of atoms and space, or void. Void is what allows motion because atoms can move through space without interference. Lucretius asserts that atoms are indivisible, solid, and indestructible, as each one moves from thing to thing.
In anticipation of protests, Lucretius disclaims the theories of the philosophers Heraclitus, Empedocles, Anaxagoras, and the Stoic objectors. Next, Lucretius explains that the universe is infinite. He illustrates this point by asking what would happen if a man went to the edge of the earth and threw a spear. The spear would, of course, go somewhere. Consequently, he reasons, atoms and void are infinite.
Lucretius explains that the differing properties of things are accounted for by the different properties of atoms. For example, substances with a bitter or harsh taste have sharper atoms than substances that have pleasant tastes. The same is true for aromas. A disagreeable scent irritates the nose as its atoms pass through, while pleasant scents are composed of smooth atoms. There are a fixed number of atomic shapes even though there are infinite atoms. Atoms are also colorless. He stresses that atoms are indestructible, but their compulsion to move on to other things creates instability in the world. He describes atomic motion as swerving. If atoms simply moved straight down, he explains, they would never collide and hence would never create anything at all.
All things must die, despite the fact that the atoms that make up a person came from another source and will become something else when the person dies. Earth provides everything humans need to live, but not forever. Lucretius concludes with the idea that there are other worlds like this one, subject to the same laws of atoms.
The atomic theories are applied to humankind as Lucretius considers the nature of the soul (which he equates with the mind). He argues that even the soul is subject to death because it is composed of atoms, which are only present temporarily. Lucretius sets out four elements of the soul's atomic composition—air, breath, warmth, and an unnamed fourth element. He claims that the soul resides in a person' s chest and is really a body part, except that the soul cannot exist without the body and vice-versa. Lucretius likens the body to ajar holding the soul; if the jar is dropped and shatters, the soul leaks out. Lucretius ends the book by reproaching those who fear death. After all, there is nothing after death, so why live in fear of nothingness? Death brings about the end of desire and is not to be mourned. Lucretius adds that all the great men who have gone before have died, so it is approaching arrogance to feel uncomfortable about following their paths. Living one's entire life in fear of death serves only to ruin what chance of happiness and peace there may be.
(The entire section is 1,365 words.)