Heraclitus was a Greek philosopher from Ephesus of Asia Minor.  He is said to have written only one book, On Nature, which was divided into three parts: concerning the All, political and theological. Today, all that is left of this book are fragments quoted by other Greek, Roman and later Christian authors.

Due to his cryptic prose, contradicting theories and fondness of wordplay (he was an admirer of the oracle of Delphi), he was known in Antiquity as ‘The Obscure’, ‘The Riddler’ or ‘The Dark One’. Another reason that made his work difficult to comprehend, was that it was written in Heraclitus’ native ionic Greek dialect.

In Heraclitus’ philosophy, everything is one. Everything comes from fire which is the fundamental element and everything is ruled by the logos, the Greek term for logic. Everything for Heraclitus is in flux, always changing. This is depicted in his famous aphorism that:

No man ever steps in the same river twice

There are two more fragments with the same idea:

Ever-newer waters flow on those who step into the same rivers.

We both step and do not step in the same rivers. We are and are not.

With these words Heraclitus also expresses the fundamental for his philosophy idea of the unity of opposites which should be understood in relation to his monism (the belief that everything in the universe comes from a single source). The unity of opposites can be best explained with the following passages:

Opposite unites. From what draws apart results the most beautiful harmony. All things take place by strife.

Upward, downward, the way is the same.

For to souls it is death to become water, and for water, it is death to become earth; but water is formed from earth, and from water, soul. 

Good and bad are the same.

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The following poem by Jorge Louis Borges is a beautiful exercise in Heraclitean philosophy. Borges perfectly captures the agony and horror of the philosopher when he comes across the constant flux of the river and is forced to face the the nature of the universe which is always a becoming. Time and existence become void of meaning in the face of this existential realisation, and Heraclitus discovers his own identity, which is not stable but like the river constantly moving. Heraclitus becomes Borjes and they become nobody. Time, place and identity merge. Heraclitus is in front of the river and the Red Cedar, he speaks words in Greek and writes them down in Spanish.

Heraclitus

To Ephesus. The afternoon has brought him,

without his will intending,

On the side of a silent river.

His destiny and his name he ignored.

There is a stone Janus and some poplars

He looks in the runaway mirror

And discovers and works the sentence

That the generations of men

Will not drop. His voice declares:

No man ever steps twice in the waters

From the same river. He stops. He feels

With the astonishment of a sacred horror

That he is also a river and a leak.

He wants to recover that morning

And his night and the day before. He can not.

He repeats the sentence. He sees it printed

In future and clear characters

In one of the Burnet pages.

Heraclitus does not know Greek. Janus,

God of the doors, is a Latin god.

Jorge Luis Borges, La moneda de hierro (1975)