Diogenes Laertios (Greek Διογένης Λαέρτιος Diogénēs Laértios, Latinized Diogenes Laertius) was an ancient historian of philosophy and doxographer. He probably lived in the 3rd century and wrote a compilation on the lives and teachings of the philosophers of antiquity, divided into ten books.
Almost nothing is known about the circumstances of Diogenes Laertios” life. Even a dating (3rd century) is only indirectly inferred from his style as well as from life dates of the philosophers he treats: The latest philosopher he mentions (IX 116) is a student of Sextus Empiricus. Otherwise, Diogenes hardly lists any philosophers of the Roman imperial period and, surprisingly, completely ignores Middle Platonism, which was predominant in his time.
From the epithet Laertios one tried to draw conclusions about the origin. Thus it was derived from the place Laerte in Caria or Cilicia or from the Roman family name Laertii. Currently, the name is usually referred to Laertes, the father of Odysseus, whom already Homer diogenes Laertiades (Διογένης means ”begotten of God”). The epithet Laertiades is therefore rather to be interpreted as a literary playful distinction from other Greeks named “Diogenes”. Biographical information cannot be derived from it.
Diogenes writes about Apollonides from Nikaia that he is someone “who comes from our corner” (IX 109). This led to the assumption that Diogenes came from Bithynia. The fact that his erudition seems ancient and that he likes to cite older and remote sources in a certain ”antiquarian tendency” would speak for an origin from the province. The work itself confirms that Diogenes possessed a certain education and knowledge, but that he was hardly an independent, critical thinker, and probably not a “specialist philosopher” who had studied in Athens or the like or had made long educational journeys.
Sometimes it was assumed that Diogenes was identical with Diogenes of Oinoanda, who was known from a larger inscription find, but this remains speculation. The argument for this was that Diogenes of Oinoanda was an Epicurean, but Diogenes Laertios dedicates an entire book to the Hellenistic philosopher and therefore, as is assumed, had sympathies for Epicureanism.
The exact title of the work, consisting of ten books and written after the middle of the 2nd century, varies somewhat in the manuscripts and editions. The most common phrases On the Lives and Teachings of Famous Philosophers or Compilation on the Lives and Teachings of Philosophers (ancient Greek φιλοσόφων βίων καὶ δογμάτων συναγωγή) already indicates the compendial character of the work, which combines biography and doxography. This compilation as doxobiography is extremely atypical, as these two literary genres were widely used in the Roman imperial period, but were strictly separated from each other.
Diogenes can hardly be assigned to a philosophical school, although it is often assumed that he was a skeptic. He seems to have been an isolated figure and to have compiled his compilation out of hobby. His work is free of polemics – as far as they were not taken from the sources – and has also left no traces in late antique literature in the form of quotations from later authors.
Diogenes thus did not intend to write a ”scientific” work. He was more interested in presenting his extensively but uncritically collected biographical news, anecdotal stories, and sentence-like expressions of opinion in an entertaining way. The work consists mainly of excerpts and quotations from third or fourth hand sources. Diogenes himself hardly seems to have read the original texts; in many cases, they were no longer extant by his time.
The identification of the sources has been the main question of research since the 19th century. Diogenes probably relied on works by Favorinus and Diocles of Magnesia, but it is not possible to prove with certainty in detail who his informants were. He probably also used collections of sayings and collections of apophthegms. Therefore, his biographical details about the lives of the ancient philosophers are rarely authentic: primarily (apart from Book X) they are anecdotes, gossip or ridicule. As a result, Diogenes” work should be used with great caution due to its uncritical nature. However, since it is the most comprehensive surviving doxographic source on the philosophy of Greek antiquity, one must nevertheless rely on Diogenes for lack of better sources.
The structure (see table) is neither systematic nor consistently arranged according to the lifetimes of the persons treated, but according to the philosophical ”schools” to which Diogenes assigns the individual philosophers according to ancient, but often rather arbitrary practice. Diogenes assumed (Book I) that there were only two philosophical trends, an ”Ionian” and an ”Italic”. He subordinates the individual philosophers to these two currents (partly not very sensibly). In the last book there are exceptionally first-hand texts, namely letters and the testament of Epicurus, for which Diogenes is in this case an excellent source.
Friedrich Nietzsche judged, “He is the night watchman of Greek philosophical history; one cannot enter it without being given the key by him.”
In the order in which Diogenes treats them, the following philosophers or authors are portrayed: Thales, Solon, Chilon, Pittakos, Bias, Kleobulos, Periander, Anacharsis, Myson, Epimenides, Pherekydes, Anaximander, Anaximenes, Anaxagoras, Archelaos, Socrates, Xenophon, Aeschines, Aristipp, Phaidon, Eukleides, Stilpon, Kriton, Simon, Glaucon, Simmias, Kebes, Menedemos, Plato, Speusipp, Xenocrates, Polemon, Krates, Krantor, Arkesilaos, Bion, Lakydes, Karneades, Kleitomachos, Aristotle, Theophrast, Straton, Lycon, Demetrios, Herakleides, Antisthenes, Diogenes, Monimos, Onesikritos, Krates, Metrokles, Hipparchia, Menippos, Menedemos, Zenon, Ariston, Herillos, Dionysios, Kleanthes, Sphairos, Chrysipp, Pythagoras, Empedocles, Epicharm, Archytas, Alkmaion, Hippasos, Philolaos, Eudoxos, Heraclitus, Xenophanes, Parmenides, Melissos, Leucipp, Democritus, Protagoras, Diogenes of Apollonia, Anaxarchos, Pyrrhon, Timon and Epicurus.
Excursus: Meaning as a source for ancient logic
Diogenes Laertios was considered the source for the knowledge of Stoic logic. Since the rediscovery of Stoic propositional logic by Jan Łukasiewicz, however, the texts in question have gained even more interest.
It is clear from the work that propositional logic did not originate with the Stoic school, but was developed by the ”dialecticians” (formerly identified with the ”megarics”). The founders of the Stoa, Zeno and Chrysippus, adopted and modified the propositional approaches of the dialecticians Diodoros Kronos and Philon of Megara.
In Diogenes one already finds a consistent doctrine of the “unprovable” arguments, which are the axioms of the Stoic propositional logic. From a passage of Diogenes” reports it even emerges that Philon represented a truth-functional theory of material implication, as it was developed after him only again by Ludwig Wittgenstein in his Logisch-philosophische Abhandlung. The work of Diogenes is also an important source for the fallacies, with which the Stoics and especially the Dialecticians dealt in great detail.