The concept of "open work", as described by Umberto Eco, owes its existence to collaborations with Luciano Berio, among others during the conception of Opera, from 1956. The openness, in Opera, consists among others in the multiplicity of meanings and in the complexity of internal and external references, in the "integration of numerous levels of perception". Passaggio, premiered in 1963, realises the Brechtian principle of the abolition of the border between scene and audience. It is a "musical action" in which the auditor has a share. However, freeing itself from narrative coherence, the musical and dramatic space elaborated by Berio appears to unveil but an introspective openness, as if to restore hearing's primordial function.