In By Being, It is, Nestor-Luis Cordero explores the richness of this Parmenidean thesis, which became the cornerstone of philosophy. Cordero's textual analysis of the poem's fragments reveals that Parmenides' intention was highly didactic. His poem applied, for the first time, an explicative method that deduced consequences from a true axiom: by being, it is. To ignore this reality meant to be a victim of opinions.