This paper explores the concept of passions from an interdisciplinary semiotic perspective, linking cognitive and neurobiological sciences to the Greimassian approach to explaining emotion. This open semiotic method moves beyond a purely textual approach to semiotics, expanding its application into psychopathology and a clinical subject. I describe the semiotics of passion and then link the idea to the semiotic square’s various theoretical uses and interpretations. Namely, through the works of Algirdas Greimas and Jaques Lacan. The subject and method are then connected to illustrate a new diagnostic technique for disease categorisation. Using a Greimas square, we explain how passion can function as a diagnostic rubric to categorise psychosis and neurosis—delimiting what does and doesn’t fit into this nosological process of categorising disease. This novel semiotics approach differs from a more traditional method, which uses clinical cases to develop a schema rather than theorising from first principles. I.e. in the Diagnostic and Statistical Manual of Mental Disorders (DSM).This approach allows us to visually map passional codes to display conditions as groups determined by the absence, presence, negation or rejection of passion. Equally, it demonstrates where clear clinical and treatment boundaries exist, such as between passion-related conditions and trauma. In effect, Greimas’ theory can be used to establish clinical thresholds and semiotic boundaries in psychological condition management. In conclusion, we offer a novel methodology rooted in semiotic logic as an alternative to the existing process of categorising diseases by expert panels.