Parmenides' importance consists in the fact that he represents an absolute beginning in history, and particularly in the history of thought. He was the first to question the meaning and the consequences of the use of the verb "to be", whose banality is equaled only by its importance in ancient Greece; by wondering about "being", we touch upon the foundations of discourse, of thought, and even of reality. We can understand why, for more than twenty years now, N.L. Cordero has devoted tremendous efforts to understanding the few verses that remain to us of this Poem, from which every trace of a middle term between "what is" and "what is not" is, provocatively, excluded. The result is the present book, characterized by its completeness and its rigor. It is an essential work on a seminal thinker.