The concept of Unitarian psychosis has a long history and goes back many centuries before the birth of psychiatry. Bartolómé Llopis, an unknown spanish psychiatrist, in the monograph devoted in 1954 to this issue, posed the question: “Is it peculiar to each disease entity a precise and specific psychological symptoms or, conversely, only it is feasible to classify symptoms like inespecific syndroms, e.g., capable of occur in any disease entities? Or what amounts to the same thing: Psychological symptoms, are produced and set in each case by its pathogenetic cause or represent only possibilities of a preexisting reaction, which can be evidenced by the causes different? ”. These words face to us with a series of concepts which can't be considered well resolved by psychopathological studies. Indeed, the author mentions the term psychosis and tells us later that the word psychosis is linked to a certain ambiguity. If we examine the historical route of the concept of psychosis and the efforts that many authors have devoted to refine its semantic field in order to establish the basis for differential diagnosis, we can notice that many treatises and manuals talk about psychosis without defining them. In some cases it is said that such disorders are characterized by their severity and serious repercussions on the individual's life. Then, we usually work with a concept lacking stringency and in no way can be accepted. We review this issue with the support of the fuzzy logic.