While distinguishing three successive steps in the making of a diagnosis, the authors point out the premises of modern semiology. They refer to the work of K. Schneider (pragmatic approach), Jaspers, Bleuler and Janzarik (approach based on theoretical concepts), Kasanin and finally Langfeldt (empirical approach). Current approaches of semiology try to define diagnostic criteria. In that line of thinking, the school of Vienna, while establishing the insufficiency of all systems, proposes the adoption of a polydiagnostic approach that would eventually define consistent semiologies that refer with certainty to real nosological entities.