Ancient Greek philosopher, perhaps best remembered for his famous poetic aphorism – "no one steps into the same river twice." Heraclitus seems to have written only one work (On Nature?), which apparently consisted of series of epigrammatic remarks. The book was deposited in the Temple of Artemis in Ephesus. Although Heraclitus's book is lost, about 120 short fragments have survived in the texts of later authors, who quoted him, often in order to scorn his ideas.

"The Ephesians deserve to have all their youth put to death, and all those who are younger still banished from their city, inasmuch as they have banished Hermodorus, the best man among them, saying, "Let no one of us be pre-eminently good; and if there be any such person, let him go to another city and another people." (in The Lives and Opinions of Eminent Philosophers, by Diogenes Laërtius, tr.  C. D. Yonge, 1853)

Little is know of Heraclitus's life. Due to his cryptic, oracular style he had a reputation for obscurity; he was something like a Wittgenstein of the Presocratics. Socrates complained that "it needs a sponge-diver to bring up the truth from those depths."

Heraclitus was born in Ephesus in Ionia (western Asia Minor) into an influential family. His father, Bloson, was a member of the highest local aristocracy. His hereditary class privileges Heraclitus renounced in favor of his brother.

Diogenes Laertios, who lived about seven centuries later, tells in Lives of and Opinions of Eminent Philosophers several anecdotes of Heraclitus. According to Laertios, Heraclitus suffered from dropsy. He "covered himself with cow-dung, hoping to cause the wet to evaporate from him, by the warmth that this produced. And as he did himself no go good in this way, he died, having lived seventy years..." Laertios also refers to Neanthes of Cyzicus who said that he was devoured by the dogs. It is generally agreed that Laertios' biographical anecdotes are not so reliable as his doxographic notions.

"... each time I recall fragment 91 of Heraclitus," wrote Jorge Luis Borges in 'A New Refutation of Time' (1944-47), "'You cannot step into the same river twice,' I admire his dialectical skill, for the facility with which we accept the first meaning ("The river is another") covertly imposes upon us the second meaning ("I am another") and gives us the illusion of having invented it..." Heraclitus taught that what we think of as things are more accurately understood as processes: "All things flow; nothing endures," he said. Aristotle further argued that if this is true, there can be no knowledge of things which are in a state of flux.

When Thales of Miletus held that water is the root of all things, Heraclitus considered fire to be the primary form of all matter. Everything is in a state of perpetual change; things come into existence and they then pass away. "All things are exchanged for fire, and fire for things; as goods for gold and gold for goods." Later the Stoics built their theory of the world and its never-ending cycles on Heraclitean principles.

Heraclitus had little sympathy for democracy, but in this he was not alone; democracy was invented by the urban Athenians, not in the prosperous Ionia. Most of the spiritual leaders of the fifth and fourth centuries, with the exception of the Sophists and Euripides, were on the side of aristocracy and reaction. In the Marxist history of philosophy Heraclitus has been an acknowledged thinker. He is regarded as one of the earliest predecessors of the Dialectical Materialism. One of its central doctrines, derived from Hegel, is that higher truths may be reached from contradictions. The underlying general law of development of nature, society, and thought is dialectic. From a battle between ideas – between thesis and antithesis – comes a synthesis, which perhaps again becomes a link in the dialectical chain. Both Hegel and Nietzsche admired Heraclitus. "There is no sentence of Heraclitus' that I have not taken into my Logik," Hegel confessed. Nietzsche said that Zarathustra's and his doctrine of the "eternal recurrence" might have been taught already by Heraclitus.

Heraclitus observed that opposites, such as living and dead, waking and sleeping, young and old, are connected by change: without one contrary the other would not exist. But the ultimate law or reality is not change. In spite of the conflicts and contradictions, there is a hidden harmony, "a tension of opposites, like that of a bow of a lyre". Thus "the way up and the way down are one and the same." The logos, the great transcendental governing principle of the universe, is common to all.

Heraclitus's logos seems to be synonymous with fire: "Fire is the underlying element: the world is an ever-living fire." The cosmos was not created by gods or mankind, "but it was ever and is and shall be ever-living Fire, kindled in measure and quenched in measure." Most mortals lack understanding of the logos. They are like sleepwalkers unaware of the reality around them. The wise, having heard the logos, agree that all things are one. Heraclitus also wrote, that "the lightning steers the universe." It can also be said, that his own fragments are similar flashes of thought – "I searched within myself," he said. The German philosopher Martin Heidegger tells in Heraclitus Seminar (1993), that on his journey in Aegina he saw suddenly a single bolt of lightning, "after which no more followed. My thought was: Zeus."

For further reading: Remembering Heraclitus by Richard G. Geldard (2000); The Origins of Epistemology in Early Greek Thought: A Study of Psyche and Logos in Heraclitus by Joel Wilcox (1994); Heraclitus Seminar by Martin Heidegger and Eugen Fink (1993); Heraklit heute by G. Nesse (1982); The Art and Thought of Heraclitus by C.H. Kahn (1979); Archaic Logic: Symbol and Structure in Heraclitus, Parmenider and Empedocles by R.A. Prier (1976); Eraclito: Testimonianze e imitazioni by R. Mondolfo and L. Taran (1972); The Pre-Socratic Philosophers by Kathleen Freeman (1966); Heraclitus by P. Wheelwright (1959); The Presocratic Philosophers by G.S. Kirk and J.E. Raven (1957); Doxographi Graeci by Hermann Diels (1879); The Lives and Opinions of Eminent Philosophers by Diogenes Laërtius (1853) - Suomennokset:   Herakleitos: Yksi ja sama, 1971 (suom. Pentti Saarikoski)

Editions:

• Ek ton Herakleitu tu Ephesiu, in Poiesis philosophos, 1573 (ed. H. Stephanus)
• Heracliti Ephesii reliquiae, 1877 (edited by I. Bywater)
• Herakleitos von Ephesos, 1909 (ed. H. Diels)
• I frammenti e le testimonianze, 1945 (ed. C. Mazzantini)
• Heraclitus: The Cosmic Fragments, 1954 (edited with an introd. and commentary by G. S. Kirk)
• Fragmente. Griechisch und deutsch, 1965 (5th ed., edited by Bruno Snell)
• Heraclitus: Greek Text with a Short Commentary, 1967 (edited by Miroslav Marcovich, 2nd ed., 2001)
• Heraclitus of Ephesus: An Edition Combining in One Volume the Fragments of the Work of Heraclitus of Ephesus On nature, 1969 (translated from the Greek text of I. Bywater by G. T. W. Patrick, introd. by Lewis A. Richards)
• Héraclite ou la Séparation, 1972 (ed. Jean Bollack and Heinz Wisman)
• Heraklit: Fragmente, 1976 (6th. ed., edited by  B. Snell)
• Eraclito: Testimonianze e frammenti, 1976 (foreword by Emilio Bodrero)
• I frammenti e le testimonianze, 1980 (translated by Carlo Diano, commentary by Carlo Diano and Giuseppe Serra)
• The Art and Thought of Heraclitus: An Edition of the Fragments, 1979 (edited and translated by Charles H. Kahn)
• Fragments / Heraclitus; A Text and Translation, 1987 (with a commentary by T.M. Robinson)
• Fragments: The Collected Wisdom of Heraclitus, 2001 (translated by Brooks Haxton, foreword by James Hillman)