The synecdoche, a close connection between the part and the whole, is fundamental in the creation of an interior Weltanshauung. As carrying out of a space inside another space is concretely made an architecture, it is essential that the stage design become an important part of architectural design. Its strong point is establishing itself, in a self-referent way, into an empty host space with a precise border: the stage project is a medium between the container and its contents, between the audience and the performance. Dream space and action space, worlds and words are mixed into an oneiric universe arisen from well-changed “notions” or “portions” of the known space. One of the better examples of it is Gio Ponti’s stage work with the continuous osmosis between his own interior design and set design. His whole work is a mix of painting, poetry, architecture and interior design. [1] Starting in the 40s, Ponti has the experience of designing sets where he sees as an opportunity to study compositions of shapes and colors that he used in his architectural design. From this experience, Ponti gained not only his identifying elements of set design, but also his recurring interior design compositions, already recognizable in numerous sketches for the theater. His ability to invert the traditional role of the stage designer from set painter to architect, and his use of the stage as a space to test new architectures, allows us to use “THEATRICALITY” in words that make up the interior world. ________________________________________ [1] He said: “there is no deviation: everything that a man does is on the same layer, on his continuity of expression” (cfr. F. Irace, “Gio Ponti. La casa all’italiana”, p. 18: “non esistono diversioni: tutto ciò che un uomo fa è sempre sullo stesso piano, nella sua continuità espressiva”).