Category: Persons

Diogenes Laertius’ Plato

The third book of Diogenes Laertius’ work is devoted to Plato. It includes a biography of the philosopher, a summary of his doctrines and an introduction to the Platonic dialogues.

The author

Diogenes Laertius’ identity remains unknown. His name may refer to his place of origin, the ancient city Laerte in Cilicia or it could be a literary pseudonym. He lived in the 3rd century CE.

Diogenes Laertius’ work

Diogenes Laertius’ work is the oldest collection of biographies of ancient Greek philosophers that has survived as a whole. As its title suggests (Lives and Opinions of Eminent Philosophers) the work is a composition of biographies of philosophers and summaries of their doctrines. It consists of ten books, each dealing either with a certain philosopher or with a particular philosophical school.

The work itself is not Diogenes’ original creation. Diogenes collects his material from earlier sources and recontextualizes them into his own project. It has been a valuable source of information about the history of ancient philosophy, especially where the original sources have been lost. Nevertheless, the validity of the information it transmits has been questioned and so it should be approached critically.

Diogenes Laertius’ Plato

The third book of Diogenes Laertius’ work is exclusively devoted to Plato. The author, contrary to his common practice of providing a biography followed by a summary of doctrines, adduces additional evidence regarding the Platonic dialogues and doctrines. This seems to be an authorial choice in order to satisfy his reader’s expectations, who is characterized as a “lover of Plato.”


The book consists of four distinct parts: 1. §1-47: Plato’s biography 2. §48-66: The Platonic dialogues 3. §67-80: Summary of Platonic doctrines 4. §80-109: Divisions


 1. §1-47: Plato’s biography

This part is one of the six surviving ancient biographies of Plato. In general it repeats the basic account of ancient biographies: birth and origin, education and youth, influences and relations to contemporary thinkers, achievements, disciples, travels and death. To these, Diogenes adds a number of anecdotes, which aim to sketch the character of the philosopher and outline a temperate and harsh personality. Diogenes focuses on the following aspects of Plato’s life:

• Plato had a divine origin, being born out of the union of a god (Apollo) and his mortal mother Perictione.

• The philosopher belonged to an aristocratic family, which familiarized him from an early age with the Athenian political life.

• Plato owns his philosophical career to his meeting with Socrates and the great impact which Socrates’ trial and death had upon him.

• Apart from Socrates, Plato’s thought was deeply influenced by Heraclitus and Pythagoras.

• Plato’s major contribution to philosophy was the original writing of philosophical dialogues and the introduction of dialectic in philosophical practice.

• Plato travelled to Sicily repeatedly, seeking to validate and actualize his philosophical beliefs.

• Plato founded the Academy, the first philosophical school. • Plato’s death was honored with a public funeral. The philosopher also left a testament, which is preserved only in Laertius’ book.

2. §48-66: The Platonic dialogues

This section is an addition to the usual structure of Diogenes’ books. Its purpose is to prepare the reader for the study of the actual Platonic works. It includes the organization of the Platonic corpus, a description of the philosophical method, notes on the Platonic terminology, suggestions on the interpretation and edition of the Platonic texts.

The subject of the arrangement of the Platonic corpus occupies the main part of this section. Diogenes presents the alternative orderings of the dialogues: a) into tetralogies, i.e. groups of four dialogues transmitted by Thrasyllus, b) to trilogies, groups of three dialogues, as it was suggested by Aristophanes of Byzantium, c) between inquiring and instructional dialogues. Diogenes also refers briefly to other arrangements, according to the proper order of reading the dialogues or depending on the kind of narration they represent.

3. §67-80: Summary of Platonic doctrines

The summary of the Platonic doctrines presented in this section is characteristic of the introductory handbooks to Platonic philosophy, circulated widely at Diogenes’ time. It is oriented towards novice students of philosophy and outlines the Platonic doctrines, focusing on natural philosophy, while ethics and dialectic receive only a concise treatment. The influence of the Platonic Timaeus is predominant in this part, which is marked by references to the dialogue’s cosmological and cosmogonic principles. The philosophical themes are presented in the following order: - The immortality of human soul - Composition and functions of the World Soul - The mathematical structure of the universe - Cosmological principles: god, matter, paradigm - Properties of the sensible world - Time and celestial bodies - Human virtues and purpose of life - Plato’s invention of dialectic

4. §80-109: Divisions

Diogenes’ divisions include more than thirty definitions of concepts, which are divided into subcategories. For example, constitutions are divided into democratic, aristocratic, oligarchic, monarchic and tyrannical. Diogenes mentions that this passage is derived from Aristotle, who supposedly attributed the divisions to Plato. Although the divisions are now considered pseudo-Aristotelian, it most probably comes from the Old Academy and thus it is one of the earliest sources found in Diogenes.

Interpretative remarks

Diogenes Laertius’ book on Plato preserves material that has not survived elsewhere, such as the philosopher’s testament. It represents a compilation of earlier sources, which are dated from the 3rd c. BCE to the 2nd c. CE. Although these sources are all reflected in the book, the primary line of influence seems to be Middle Platonist. Furthermore, the biographical section of the book is far more elaborated than the philosophical ones; the latter contain obvious oversimplifications and contradictions. This might have been the result of the author’s attempt to adjust his material to the needs and expectations of his philosophically inexperienced reader.

Author: Spyros Benetatos
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  • Brisson, L. "Amélius: Vie, œuvre, doctrine." ANRW ΙΙ 36.2 (1987)
  • Mejer, J. Diogenes Laertius and his Hellenistic Background. Hermes 40. Wiesbaden, 1978.
  • Mansfeld, J. Prolegomena: Questions to be Settled before the Study of an Author or a Text. Leiden, 1994.
  • Riginos, A.S. Platonica. The Anecdotes Concerning the Life and Writings of Plato. leiden, 1976.
  • Baltes, M., Dörrie, Η. Der Platonismus in der Antike. Band 3: Der Platonismus im 2. und 3. Jahrhyndert nach Christus. Stuttgart, 1993.
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