1. Sources
The major source for Epicurean doctrine is Diogenes Laertius' third-century C.E. Lives of Eminent Philosophers, a compilation of information on the lives and doctrines of the philosophers of classical Greece (see “Doxography of Ancient Philosophy”). In the tenth and final book, devoted to Epicureanism, Diogenes preserves three of Epicurus' letters to his disciples, in which he presents his basic views in a concise and handy form. The Letter to Herodotus summarizes Epicurus' physical theory, the Letter to Menoeceus offers a précis of Epicurean ethics, and the Letter to Pythocles treats astronomical and meteorological matters. (There is some doubt about whether the last is by Epicurus himself or a follower, but there seems to be sufficient reason to attribute it to the founder himself.) Diogenes also quotes a collection of brief sayings, called the “Principal Beliefs” or “Principal Doctrines” (Kuriai Doxai), excerpted from the writings of Epicurus or, in some cases, of his close associates; another such collection, partially overlapping with the first, survives in an independent manuscript and is conventionally called the Vatican Sayings. The purpose of both sets, like that of the Letters, was to make the core doctrines easy to remember. Diogenes also fills in topics not covered in the Letters, and provides a list of Epicurus' writings and other biographical information.
Short citations of Epicurus' works appear in other writers (e.g., Plutarch, Sextus Empiricus, and the Greek commentators on Aristotle), often taken out of context or presented in a polemical and distorted fashion. (The standard edition of Epicurus' works in Greek is Arrighetti 1973; the fullest collection of fragments and testimonies is still Usener 1887, repr. with Italian translation, Ramelli 2002; for translations, see Bibliography: Editions, Translations, Commentaries). In addition, several works of Epicurus, including parts of his major treatise, On Nature (Peri phuseôs) — a series of lectures running to 37 papyrus rolls — have been recovered in damaged condition from the library of a villa in the town of Herculaneum, which was buried in the eruption of Mt. Vesuvius in 79 C.E. The library almost certainly contained the working collection of Philodemus, an Epicurean philosopher from Syria who studied in Athens and moved to Italy in the first century B.C.E. Many of the rolls consist of Philodemus' own writings, and provide valuable information about later issues in the history of Epicureanism. One must be cautious about ascribing these views to the founder himself, although the school tended to be conservative and later thinkers embellished rather than altered Epicurus' own teachings. New editions and translations are now making these difficult texts available to a wider readership.
More or less contemporary with Philodemus is Lucretius (first century B.C.E.), who composed in Latin De rerum natura (“On the Nature of Things”; the title, if it is Lucretius' own, is an adaptation of “On Nature”) in six books of hexameter verse, the meter characteristic of epic and didactic poetry. As a dedicated Epicurean, passionate to promulgate the message of the founder, Lucretius reproduced Epicurean doctrine faithfully (Sedley 1998; Clay 1983 allows Lucretius more originality). His poem concentrates principally on the physical and psychological or epistemological aspects of Epicureanism, and to a great extent omits the ethical. From a hostile point of view, Cicero rehearsed and criticized Epicurus' ideas, especially concerning ethics, in several of his philosophical works, including On Moral Ends (De finibus) and the Tusculan Disputations. Still later, in the second century C.E., another Diogenes erected a large inscription, to this day only partially excavated, in the city of Oenoanda (in southwestern Turkey), which contained the basic tenets of Epicureanism (authoritative edition by Smith 1993, but new fragments have been published subsequently; see also Gordon 1996).
2. Life
“Epicurus, the son of Neocles and Chaerestrata, was an Athenian from the deme of Gargettus and the lineage of the Philaïdes, as Metrodorus says in his On Noble Families. Heraclides, among others, in his epitome of Sotion, says that he was raised in Samos, since the Athenians were given parcels of land there, but came to Athens when he was eighteen, when Xenocrates was head of the Academy and Aristotle was still in Chalcis” (where he died in 322). So begins the account by Diogenes Laertius (10.1). The dates for Epicurus' birth and first move to Athens are thus 341 B.C.E. and 323 respectively. Diogenes adds that after the death of Alexander (323), when the Athenians were expelled from Samos, Epicurus left Athens and joined his father in Colophon (in 321), on the coast of what is now Turkey. Here he studied philosophy under the tutelage of Nausiphanes, a Democritean philosopher with skeptical leanings, and author of a work called the Tripod, on which Epicurus reportedly drew for his Canon, his principal work on epistemology; in ethics, Nausiphanes substituted the term akataplêxia (“undauntability”) for Democritus' athambiê, “fearlessness,” as crucial to the good life, which invites comparison with Epicurus' ataraxia or “imperturbability,” though Epicurus is said to have denied having been influenced by him (On Nausiphanes' role in transmitting elements of Democritean doctrine to Epicurus, see Warren 2002: 160–92.)
Ten years later, Epicurus moved to Mytilene on the island of Lesbos, and soon proceeded to Lampsacus on the nearby mainland; in both cities he taught and gathered followers before returning again to Athens in 307/06, where he remained until his death in 270, at the age of seventy or seventy-one. In Athens, he purchased the property that became known as the “Garden” (later used as a name for his school itself) and began to develop his own school in earnest. Diogenes reports a number of slanderous stories that were circulated by Epicurus' opponents, despite which he affirms that Epicurus was of an extraordinarily humane disposition; this was the prevailing view, shared even by hostile witnesses to Epicureanism. Diogenes also records Epicurus' will (10.16–21), in which, among other things, he made provisions for the children of his friends and appointed a successor.
3. Physical Theory
Epicurus held that the elementary constituents of nature are undifferentiated matter, in the form of discrete, solid and indivisible particles (“atoms”) below the threshold of perception, plus empty space, that is, the complement of matter or where matter is not (Inwood 1981, Konstan 2014; contra Sedley 1982, who argues that space, for Epicu