structural:summarization, quality:correction
The Obscure

Aristotle quotes part of the opening line of Heraclitus's work in the Rhetoric to outline the difficulty in punctuating Heraclitus without ambiguity; he debated whether "forever" applied to "being" or to "prove". Aristotle's successor at the lyceum Theophrastus says about Heraclitus that "some parts of his work half-finished, while other parts a strange medley". Theophrastus thought an inability to finish the work showed Heraclitus was melancholic.

Diogenes Laërtius relays the story that the playwright Euripides gave Socrates a copy of Heraclitus's work and asked for his opinion. Socrates replied: "The part I understand is excellent, and so too is, I dare say, the part I do not understand; but it needs a Delian diver to get to the bottom of it."

Also according to Diogenes Laërtius, Timon of Phlius called Heraclitus "the Riddler" (αἰνικτής; ainiktēs) a likely reference to an alleged similarity to Pythagorean riddles. Timon said Heraclitus wrote his book "rather unclearly" (ασαφεστερον; asaphesteron); according to Timon, this was intended to allow only the "capable" to attempt it. By the time of Cicero, this epithet became in Greek "The Dark" (ὁ Σκοτεινός; ho Skoteinós) or in Latin "The Obscure" as he had spoken nimis obscurē ("too obscurely") concerning nature and had done so deliberately in order to be misunderstood. The obscurity was "probably with the idea that it is for us to seek within ourselves, as he sought for himself and found".

Heraclitus seemed to pattern his obscurity after oracles. Heraclitus did state "nature loves to hide" and "a hidden connection is stronger than an obvious one". He also stated "The lord whose oracle is in Delphi neither speaks nor conceals, but gives a sign." Heraclitus is the earliest known literary reference to the Delphic maxim to know thyself.