A Dictionary of Music and Musicians/Act
ACT. A section of a drama having a completeness and often a climax of its own. Though the word Act has no representative in Greek, the division indicated by it was not unknown to the ancient theatre, where the intervention of the chorus stopped the action as completely as the fall of the curtain in the modern. The 'Plutus' of Aristophanes, the earliest Greek play from which the chorus was extruded, has come down to us without breaks or divisions of any kind; practically, therefore, it is 'in one act.' Whether the earlier essays of Roman dramatists were divided into acts by themselves is uncertain. The canon of Horace, that a drama should consist of neither more or less than five acts ('Epist. ad Pisones,' 189), was doubtless drawn from previous experience and practice.
The number of acts into which the modern drama is divided, though of course largely dependent on the subject, is governed by many considerations unknown to the ancient, in which 'the unities' of place as well as of time and action was strictly observed. With us the locality generally changes with each act, frequently with each scene. For this change the convenience of the mechanist and even of the scene-shifter has to be consulted. In the musical drama other considerations beside these add to the difficulties of laying out the action; such as variety and contrast of musical effect, and the physical capabilities of the performers, whose vocal exertions must not be continued too long without interruption. It is not surprising therefore that operas, even of the same class, present examples of every kind of division. French 'grand opera' consists still generally, as in the days when Quinault and Lully worked together, of five acts; French 'opéera comique' of three, and often one only. The Italians and Germans have adopted every number of acts, perhaps most often three. In performance the division into acts made by the author or composer is frequently changed. Mozart's 'Nozze di Figaro,' originally in four acts, is now generally played in two; and Meyerbeer's 'Huguenots,' originally in five, in four.
The curtain let down between the acts of a drama is called in the theatre 'the act drop.'
Handel (Schoelcher, 288, etc.) applies the word to oratorios, and it is used by J. S. Bach in a manner probably unique. He heads his cantata 'Gottes Zeit ist das allerbeste Zeit' with the words ' Actus Tragicus.' It is what would be called among ourselves a funeral anthem.