His teaching, as we have it now, is a series of epigrams. that is, sayings and remarks, rather than systematic essays. Heraclitus is famous for his doctrine of change being central to the universe. His famous sayings, "All is flux", and "You cannot step twice into the same river" is still remembered today. Another of his sayings appeals to some psychologists:
"You cannot discover the depths of the psyche, even if you travelled every road to do so, such is the depth of its meaning".
Often it is difficult to understand what he saying. He believed in the unity of opposites, stating that "the path up and down are one and the same". His utterance that "all things come to be in accordance with this logos," (literally, "word," "reason," or "account") has been the subject of many interpretations.
"Good and bad are the same". In many of these 'opposite ends' pairs, if the one never happened, then the other would be meaningless.
Diogenes Laërtius states that Heraclitus' work was "a continuous treatise On Nature, but was divided into three discourses, one on the universe, another on politics, and a third on theology." Theophrastus says (in Diogenes) "... some parts of his work are half-finished, while other parts make a strange medley".
Diogenes also tells us that Heraclitus deposited his book as a dedication in the great temple of Artemis, the Artemisium, one of the largest temples of the 6th century BC, and one of the Seven Wonders of the Ancient World. Ancient temples were regularly used for storing treasures, and were open to private individuals under exceptional circumstances. Many later philosophers refer to the work.