Book X of Diogenes Laertius preserves three letters of Epicurus and the Principal Doctrines, while the Letter to Menoeceus offers a concise ethical outline.
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This is an evidence-linked editorial paraphrase, not a direct quotation.
Epicurus
Stanford Encyclopedia of Philosophy
Locator: Section 1
Open sourceLetter to Menoeceus
Epicurus · Robert Drew Hicks historical English translation; MIT Internet Classics Archive
Locator: Sections 122–135
Open sourcePrincipal Doctrines
Epicurus · Robert Drew Hicks historical English translation; MIT Internet Classics Archive
Locator: Collection structure
Open source