O Legal positivism is a complex paradigm. Understanding it in various versions and, above all, by the medium of the rationality standards that underpin it throughout its history is one of the challenges of the theory of the right of interpretation. This critical test seeks to confront the contemporary Juspositivism from one of the main theory of this same line of thought: Hans Kelsen. The text begins with two short sections. One about the genealogy of positivism and the other about how Kelsen managed to develop a Law Science. After, the discussion goes back to the following flaws of the legal position in hodierno: (1) the absence of metalinguage; (2) the absence of concern about the difference between causality and imputation; (3) the paradox or self-contradictory approach.