This conceptual reconstruction work inscribes itself in the history of linguistics, or, more precisely, in the history of the Geneva School of general linguistics. It brings new light on the identity of this school through the comparative study of the theories developed by Charles Bally, Albert Sechehaye and Henri Frei between 1900 and 1940. Being the subject of various conceptual elaborations, both diversified and confluent, the expression and expressivity categories illustrate to what extent their ways of representing this problematic may converge or diverge. Additionally, the homogeneity effect emerging offers a new image of Ferdinand de Saussure's legacy, as reflected in the theories developed by his successors of the Geneva School.