gods live in what is called the metakosmia, or the space between worlds. Contrarily, the idealist (sometimes called the “non-realist position” to avoid confusion) position holds that the gods are just idealized forms of the best human life, and it is thought that the gods were emblematic of the life one should aspire towards. The debate between these two positions was revived by A. A. Long and David Sedley in their 1987 book, The Hellenistic Philosophers, in which the two argued in favour of the idealist position. While a scholarly consensus has yet to be reached, the realist position remains the prevailing viewpoint at this time. Epicurean writings On Nature On Nature () is the name of a philosophical treatise in 37 books consisting of lectures written by Epicurus, which can be considered his main work, however, it has mostly been lost. Some excerpts have survived compiled from burnt papyri scrolls found in the Villa of the Papyri at Herculaneum. Most of the surviving papyri are kept in the National Library of Naples. Important parts of Book II are preserved in the British Museum. Since most of the 37 books "On Nature" are lost, the Principal Doctrines and Epicurus' Letters to Herodotus, Menoeceus, and Pythocles are the most authoritative writings on Epicureanism. Similarly, Lucretius' poem De rerum natura probably follows Epicurus' work. Principal doctrines The Principal Doctrines are forty authoritative conclusions set up as official doctrines by Epicurus, Metrodorus of Lampsacus, Hermarchus of Mitilene and Polyaenus of Lampsacus. The Principal Doctrines exemplify the Epicurean philosophers' practice of publishing summaries and outlines of their teachings for easy memorization. However, they are so concise and short that it's difficult to understand them in depth without the context of additional commentaries and writings by ancient sources or by modern Epicurean practitioners, whenever possible.They are often cited as "PDs" in English. Some of the Principal Doctrines are organized into groups and are meant to be studied together. The first four doctrines make up the Tetrapharmakos (Four Cures). PD's 10-13 discuss the Epicurean philosophy of science. PD's 18-21 explain the natural limits of desires and in time, and how the flesh is unable to learn these limits but the mind can. PD's 22-25 deal with the importance of the canon, or the Epicurean standard of truth. PD's 31-38 explain the Epicurean doctrines on justice based on mutual advantage and contractarianism. PD's 39-40 call for an