Diogenes Laertius
Overview
 
Diogenes Laertius was a biographer of the Greek
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....

 philosophers. Nothing is known about his life, but his surviving Lives and Opinions of Eminent Philosophers
Lives and Opinions of Eminent Philosophers
Lives and Opinions of Eminent Philosophers is a biography of the Greek philosophers by Diogenes Laërtius, written in Greek, perhaps in the first half of the third century AD.-Overview:...

is one of the principal surviving sources for the history of Greek philosophy.
Nothing is definitively known about his life. He must have lived after Sextus Empiricus
Sextus Empiricus
Sextus Empiricus , was a physician and philosopher, and has been variously reported to have lived in Alexandria, Rome, or Athens. His philosophical work is the most complete surviving account of ancient Greek and Roman skepticism....

 (c. 200 AD), whom he mentions, and before Stephanus of Byzantium
Stephanus of Byzantium
Stephen of Byzantium, also known as Stephanus Byzantinus , was the author of an important geographical dictionary entitled Ethnica...

 and Sopater
Sopater of Apamea
Sopater of Apamea , was a distinguished sophist and Neoplatonist philosopher.He was a disciple of Iamblichus, after whose death Sopater of Apamea (d. before 337), was a distinguished sophist and Neoplatonist philosopher.He was a disciple of Iamblichus, after whose death Sopater of Apamea (d. before...

 (c. 500 AD), who quote him. His work makes no mention of Neoplatonism
Neoplatonism
Neoplatonism , is the modern term for a school of religious and mystical philosophy that took shape in the 3rd century AD, based on the teachings of Plato and earlier Platonists, with its earliest contributor believed to be Plotinus, and his teacher Ammonius Saccas...

, even though it is addressed to a woman who was "an enthusiastic Platonist." It is probable that he flourished in the first half of the third century, during the reign of Alexander Severus
Alexander Severus
Severus Alexander was Roman Emperor from 222 to 235. Alexander was the last emperor of the Severan dynasty. He succeeded his cousin Elagabalus upon the latter's assassination in 222, and was ultimately assassinated himself, marking the epoch event for the Crisis of the Third Century — nearly fifty...

 (222–235) and his successors.

The precise form of his name is uncertain.
Quotations

When Thales was asked what was difficult, he said, "To know one’s self." And what was easy, "To advise another."

Thales, 9.

He said that men ought to remember those friends who were absent as well as those who were present.

Thales, 9.

The apophthegm "Know thyself" is his.

Thales, 13. Compare" "There are two sentences inscribed upon the Delphic oracle, hugely accommodated to the usages of man’s life: 'Know thyself', and 'Nothing too much'; and upon these all other precepts depend", Plutarch, Consolation to Apollonius.

Writers differ with respect to the apophthegms of the Seven Sages, attributing the same one to various authors.

Thales, 14.

Solon gave the following advice: "Consider your honour, as a gentleman, of more weight than an oath. Never tell a lie. Pay attention to matters of importance."

Solon, 12.

As some say, Solon was the author of the apophthegm, "Nothing in excess."

Solon, 16.

 
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