De rerum natura (On the Nature of Things) by Titus Lucretius Carus

Lucretius' masterpiece De rerum natura is acknowledged as the preeminent presentation of Epicurean philosophy. How Lucretius came to learn about Epicureanism is uncertain, and there is no evidence of a specific teacher who guided Lucretius' philosophical development. Because Greek professors lectured on the teachings of Epicurus in Rome at the time, however, it is clear that he was well instructed. Epicureanism is based on four central ideas, which are that the gods are not frightening, there is nothing to fear in death, good is accessible, and bad bearable. Epicurus and his followers formed small communities of like-minded friends who gathered in gardens to study and discuss philosophical issues. Historians note that these communities were especially noteworthy for their surprising inclusion of women and slaves. Studying science and the physical world, Epicurus found support for his ideas in nature. In his epic poem, Lucretius brings together Democritus' and Leucippus' theories of "atomism" (which guided Epicurus' philosophies regarding the physical world) and Epicurus' teachings on atomic properties and moral living. Lucretius' achievement is in bringing these ideas together into a coherent philosophy of rationalism and a virtuous lifestyle.

Central to Epicurean thought is atomic theory. Epicurus learned much from the early scientific theorists Democritus and Leucippus after realizing that their physics supported his beliefs about the absence of divine intervention. This, in turn, had a profound effect on his beliefs regarding morality. The atomists also taught that reality is accessible to anyone through sense perception; the world can be understood without resorting to divine explanations for natural occurrences. The Epicureans' major contribution to atomic theory was the notion of an imperceptible movement called "swerve." Lucretius explains in De rerum natura that atoms do not fall straight down to the earth, but fall in a swerving path. This allows them to collide and combine with each other, resulting in the creation of objects and beings. In Book Two, Lucretius explains, "When the atoms are carried straight down through the void by their own weight ... they swerve a little ... For if atoms did not tend to lean, they would / Plummet like raindrops thorough the depths of space, / No first collisions born, no blows created, So / Nature never could have made a thing." Unfortunately, there is no explanation of why or how atoms swerve.

From Epicurus' cosmology came his views on morality and ethical living. In order to live fully, he claimed, it was necessary to observe and study one's natural surroundings. Epicurus designated three types of desire, the first and most important of which is natural and essential desire. This is desire for necessities, such as food, shelter, and clothing. Necessary desires are generally the easiest desires to fulfill. The second type is natural and unnecessary desire, such as sexual desire. The third type is unnatural...