Summary The birth of the rational speculation in the ancient Greece is a decisive event for the history of the western culture. Its deeper sense bases in that the human mind applies by first time the natural criteria, logical and empirical, to explore the whole what is real, as if that was susceptible of evidenciable reconstruction and from the supposed that such reality was possessing an immanent order. That supposed Greek persists as essence of the westem rationality and brand an irreversible break with the myth. Tales de Mileto is the emblematic figure of such event and, as a first philosopher, built the first philoshophemas and the first naturalist hypothesis to explain the order of the cosmos.