Jaime Alazraki's proposal on the neofantastic has tried to replace the fantastic from the landscape of the transgressive short story review in the postmodern framework. We propose a review of the transgression values through an approach to the genre from a semantic perspective. In order to support our hypothesis we work with possible worlds semantics as a method to assert the fantastic's validity in the 20th century second half. At last, we develop an impossibility typology which contains all the transgression shapes on traditional and postmodern fantastic, to assert that our method works.