Know philosophy as radical is a radical knowledge in two ways: * by seeking to understand the root of the origin of things. * For your desire to understand and explain the totality of human reality. The means by which philosophy has to do are: * the experience data that is received through the senses. * The thought understood as logical reasoning, you have to order them and unify them. The truth as knowledge of reality: the pre-Socratic philosophers first understood that the first issue that should explain the philosophy was the source of all reality, the origin of nature. The truth as knowing how to live well, but Greek philosophy also deals with the truth well understood as moral aspiration and happiness. This shift of interest is known as anthropological turn, and was led by Socrates and the Sophists in the V century BC.