Sources:

Principle Doctrines

The Principle Doctrines (Κyriai Doxai in Greek) are found in Lives and Opinions of Eminent Philosophers by Diogenes Laertius.

There are forty so-called Principle Doctrines — the list comes to us as a part of Diogenes Laertius, but the numbering system (#1-40) is not actually found in the original text. Instead the enumeration is a modern standard used since the 19th century.

Their authenticity is attested to in other works of antiquity1.

1 These are compiled by Hermann Usener and taken from Epicurism.info and stored here for safekeeping:

Diogenes Laertius, Lives of Philosophers, X.29 (Epicurus): Among the writings of Epicurus, the following are his best … Principal Doctrines … Ibid., 138: So then, let us put a seal, as they say, to my entire work and to this philosopher by relating below his Principal Doctrines, closing my entire work by making the end of it the beginning of happiness.
Philodemus, On Anger, Column XLIII, Vol. Herc. alt. coll. I.66 p. 143 [Gomperz]: … like some who, criticizing the Principal Doctrines in their writings, will act absolutely surprised that one might have the audacity to assert that anger, gratitude, and any similar feeling stem from weakness {c.f. PD 1}, while Alexander, who was more powerful than anyone else, was frequently subject to anger and demonstrated gratitude towards innumerable persons.

Uncertain Epicurean Author, Column XV Vol. Herc. (2) alt. coll. XI.34, edited by Comparetti, Fragments of Epicurean Ethics, p. 19 [Rivista di filogogia, 7, p. 417]: We must also, accordingly, speak to the matter of external factors which contribute towards fame, to precisely establish what significance they might have to us, as for example: luxury, beauty, wealth in general, and marriage – as we have already mentioned. It is also for this reason also that they are dealt with in the Principal Doctrines, and would also say that…

Uncertain Epicurean Author, Vol. Herc. (2) alt. coll. VII.21, Column XXVII: now, as for that which is closest to the matter at hand, we remain faithful to a book, having the title Principal Doctrines. Therein, Epicurus shows that that which is imperishable, by nature, insofar as the end… when he says …

Cicero, On The Nature of The Gods, I.30.85 (Cotta to Velleius): In that selection of his concise sayings, which you call the Principal Doctrines, this, I believe, is his first: {proceeds to cite PD 1}.

Cicero, On the Laws, I.7.21: Nor indeed can the Epicureans stand it, and will become very agitated, if they hear that you have betrayed the first maxim of that superlative work in which he wrote that “God doesn’t trouble himself about anything – neither his own concerns nor those of others.” [PD 1]

Cicero, On Ends, Good and Bad, II.7.20: In another book, containing a compendium of his most important doctrines, we are told he had expressed the very oracles of wisdom. Therein he writes the following words, (which surely you know, Torquatus, for who among you has not learned Epicurus’ Principal Doctrines – maxims that, notwithstanding their conciseness, are extraordinary useful for living happily?) [he proceeds to cite PD 10]

Diodorus Siculus, Historical Library, XXV fragment 1, Dind.: The philosopher Epicurus, in those works of his entitled Principal Doctrines…

Plutarch, Against Colotes, 31, p. 1125E: … in the first of the Principal Doctrines, [PD 1], they directly subvert it [the social cohesion afforded by religion].

Lucian, Alexander the Oracle Monger, 47: In this connection [railing against Epicurean debunkers] Alexander once made himself supremely ridiculous. Coming across Epicurus’ Principal Doctrines, the most admirable of his books, as you know, with its terse presentment of his wise conclusions, he brought it into the middle of the marketplace, there burned it on a fig wood fire for the sins of its author, and cast its ashes into the sea. He issued an oracle on the occasion: “The dotard’s maxims to the flames be given.” The fellow had no conception of the blessings conferred by that book upon its readers, of the peace, tranquillity, and independence of mind it produces, of the protection it gives against terrors, phantoms, and marvels, vain hopes and insubordinate desires, of the judgment and candor that it fosters, or of its true purging of the spirit, not with torches and squills and such rubbish, but with right reason, truth, and frankness.

Diogenes Laertius, Lives of Philosophers, X.31 (Epicurus): In the Canon, Epicurus specifically says that the standards of truth are the sensations, the preconceptions, and the passions. The Epicureans generally include mental impressions also. His own statements may be found in the summary addressed to Herodotus, and in the Principal Doctrines. [PD 24]

Alciphron, Letters of Courtesans, 17.II.2 (Leontium depicted writing to Lamia): How long can one suffer this philosopher? Let him keep his books On Nature, the Principal Doctrines, The Canon, and, my lady, let me be mistress to myself, as Nature intended, without anger and abuse. Ibid., 7: Some flatter him and go about singing the praises of his Doctrines.

Aelian (Claudius Aelianus), On Providence, fragment 61 [Suda, under Epicurus and klaein]: And the book had contained the doctrines of Epicurus which he called his Principal ones – Epicurus’ wicked sayings. Among these, indeed, there were also the following claims: that Creation was established by chance and not from the will and justice of God. Then, these rather celebrated atoms, by colliding with one another and then dispersing, formed the air, the earth, and the sea. Then the assemblies and compounds disintegrate and completely disappear, dissolving into atoms. All of creation, then, arises through necessity and happenstance, with no basis in the wisdom of the Creator. Moreover, Epicurus maintains that everything combined itself together without providence, without a helmsman, nor guide, nor shepherd… That one, however, sacrificed to the gods, and sent Epicurus and his Doctrines to the devil.