The world of reasoning, of the mind, and the world of experience, of the senses, as the sixth century moved into the fifth, became separate, distinct. The most outspoken critic of Xenophanes and Pythagoras was another Ionian, Hericlitus. Much information does not teach wisdom, he said, else it would have taught Pythagorus, who, from his polymathy made up an art of mischief. The perpetual motion of Anaximenes divine fire was a description of the source of change in the universe. Hericlitus said that perpetual motion was the universe. The world of Anaximander was created out of the conflict of opposites and change was derived through strife. Hericlitus said that the universe was nothing but conflict and strife. What was experienced was illusion. What there is, is a constant incessant flux, a raging fire. What is real is the logos, that which lies beneath the fire. Most of what we know about Hericlitus comes second hand and often from doubtful sources. However, it is not what he said specifically that makes him important for our study of western philosophy. It is what is implicit in his view that others could not refute. The greatest problem with Hericlitus' ideas is that they make a kind of diabolical sense. Remember that Anaximander's concept of the boundless explained the perceptible by the imperceptible. Yet, if it is not perceptible what right do we have to say it exists. Hericlitus' statements posed the greatest challenge that Greek philosophy had to struggle with. Consider this; If everything we interact with is constantly changing we can never know anything about it because once we learned anything about it, it would change and become something else. At the same time scientific knowledge, as conceived by the Greeks, is knowledge that cannot be different than it is. Thus, scientific knowledge is not possible.