Diogenes Laertius

Diogenes Laertius probably lived in the first half of the third century AD, though even this is uncertain. Nothing reliable is known about his life — not his birthplace, his education, or his philosophical allegiances. His name suggests a connection with Laerte in Cilicia, but this is speculation.

His work, Lives and Opinions of Eminent Philosophers (Vitae philosophorum), is one of the most important sources for the history of ancient philosophy. In ten books, he surveys the major philosophical schools from Thales to Epicurus, providing biographical anecdotes, summaries of doctrines, lists of writings, and occasional quotations. His treatment is anecdotal rather than analytical — he collects stories and sayings rather than reconstructing arguments.

The quality of his work varies enormously. Some lives are thin compilations of dubious anecdotes; others preserve invaluable material found nowhere else. Book X, on Epicurus, includes three complete letters and the Principal Doctrines — virtually everything we have of Epicurus' own words survives because Diogenes copied them. For this alone, the history of philosophy owes him an enormous debt.