This paper focuses on the notion of musical institution, which seems accurate to describe a tension between, on the one hand, the affirmation by the institution of a logic of its own, of a will to withdraw from the political sphere, and, on the other hand, an unavoidable implication in this sphere, because of its public status. From the fall of the Second Empire to the end of the Commune, the Paris Opera has tried to preserve, individually and collectively, the continuity of a world which represents itself as apart and out of the political sphere : during this period of uncertainty, the members of the Opera have reasserted the necessity to resume the repetitions, to preserve the unity and the hierarchical order of the institution, to go on singing the same repertoire. But, if the Republicans did not hasten to reorganize the Opera and to break up with this symbol of the previous regime, the Parisian Commune tried to build something new and to use the Opera as a political tool : against this will there was no strong political counterpart or organized opposition, but the passive resistance of a corporation which ends being political only because it refuses a very definitional element of politics, which is change.