Antisthenes c. 445 BC – c. 365 BC

Antisthenes of Athens was an ancient Greek philosopher of the 5th and 4th centuries BC, a student of Socrates and traditionally regarded as the founder of the Cynic school of philosophy. He taught at the Cynosarges gymnasium in Athens, possibly the source of the school's name through the Greek kunikos meaning dog-like. His ethics emphasised virtue as the only good, self-sufficiency as its outward sign, and the rejection of conventional desires for wealth, fame, and pleasure. His teaching that virtue is sufficient for happiness anticipates the central thesis of the later Stoics. Most of his many writings are lost; his ideas survive in fragments and in the report of Diogenes Laertius.

Antisthenes was born around 445 BC in Athens; his mother is said by ancient sources to have been a Thracian, which deprived him of full Athenian citizenship. After studying rhetoric with Gorgias he attached himself to Socrates, walking, the tradition reports, the long road from the Piraeus daily to attend his teacher's conversations, and was present at the death of Socrates in 399 BC.

He set up a school of his own in the Cynosarges gymnasium, outside the walls of Athens, that gave Cynicism its name and its early shape. Diogenes Laertius preserves a long list of his writings — dialogues, ethical and rhetorical treatises, exegeses of Homer — but only fragments survive, transmitted by Xenophon, Plato, and the later Cynic and Stoic tradition. He is one of the speakers in Xenophon's Symposium and figures memorably in his Memorabilia.

Antisthenes taught that virtue is sufficient for happiness, that virtue can be taught, and that pleasure is to be scorned; he combined sharp ethical austerity with logical and grammatical reflections, including the famous denial that contradiction is possible. Whether or not he was literally the teacher of Diogenes of Sinope, the line of transmission from Socrates to Antisthenes to Diogenes to Crates and finally to Zeno of Citium was understood in antiquity as the genealogical backbone of Cynicism and early Stoicism. He died in Athens around 365 BC.