<P> Heraclitus was famous for his insistence on ever - present change as being the fundamental essence of the universe , as stated in the famous saying , `` No man ever steps in the same river twice '' ( see panta rhei below ) . This is commonly considered to be one of the first digressions into the philosophical concept of becoming , and has been contrasted with Parmenides statement that `` what - is is '' as one of the first digressions into the philosophical concept of being . As such , Parmenides and Heraclitus are commonly considered to be two of the founders of ontology . Scholars have generally believed that either Parmenides was responding to Heraclitus , or Heraclitus to Parmenides , though opinion on who was responding to whom changed over the course of the 20th century . Heraclitus ' position was complemented by his stark commitment to a unity of opposites in the world , stating that `` the path up and down are one and the same '' . Through these doctrines Heraclitus characterized all existing entities by pairs of contrary properties , whereby no entity may ever occupy a single state at a single time . This , along with his cryptic utterance that `` all entities come to be in accordance with this Logos '' ( literally , `` word '' , `` reason '' , or `` account '' ) has been the subject of numerous interpretations . </P>
<P> Heraclitus was famous for his insistence on ever - present change as being the fundamental essence of the universe , as stated in the famous saying , `` No man ever steps in the same river twice '' ( see panta rhei below ) . This is commonly considered to be one of the first digressions into the philosophical concept of becoming , and has been contrasted with Parmenides statement that `` what - is is '' as one of the first digressions into the philosophical concept of being . As such , Parmenides and Heraclitus are commonly considered to be two of the founders of ontology . Scholars have generally believed that either Parmenides was responding to Heraclitus , or Heraclitus to Parmenides , though opinion on who was responding to whom changed over the course of the 20th century . Heraclitus ' position was complemented by his stark commitment to a unity of opposites in the world , stating that `` the path up and down are one and the same '' . Through these doctrines Heraclitus characterized all existing entities by pairs of contrary properties , whereby no entity may ever occupy a single state at a single time . This , along with his cryptic utterance that `` all entities come to be in accordance with this Logos '' ( literally , `` word '' , `` reason '' , or `` account '' ) has been the subject of numerous interpretations . </P>
who said you ca n 't step into the same river twice
who said you ca n 't step into the same river twice
Heraclitus
Heraclitus