The pre-Socratic Greek philosopher Parmenides taught that the only things that are real are things which never change... and the pre-Socratic Greek philosopher Heraclitus taught that everything changes. If you superimpose their two views, you get this result: Nothing is real. There is a fascinating next step to this line of thinking: Parmenides could never have existed because he grew old and died and disappeared, so, according to his own philosophy, he did not exist. And Heraclitus may have been right -- let's not forget that; so if Heraclitus was right, then Parmenides did exist, and therefore, according to Heraclitus' philosophy, perhaps Parmenides was right, since Parmenides fulfilled the conditions, the criteria, by which Heraclitus judged things real.