And yet we must go back to the Greek theater if we want to see why it is that the 'Femmes Savantes' of Molière and the 'School for Scandal' of Sheridan are each of them in five acts. But it is not from a Greek that we get the law that this division was obligatory on all self-respecting dramatists; it is from a Roman, writing at a time when the drama of his own language had been ousted from the stage by pantomimic spectacle and by gladiatorial combat. It is Horace, who, in his epistle on the art of poetry, declares the necessity of five acts:
Ne brevior, neu sit quinto productior actu Fabula quae posci vult et spectata reponi.
Sir Theodore Martin rendered this in an English rimed couplet, which does not completely convey the meaning of the two Latin lines, but which will serve to show the rigidity of the rule laid down by the Roman poet:
Five acts a play must have, nor more nor less, To keep the stage and have a marked success.
But this still leaves us groping in the dark. Why did Horace declare this law? What warrant had he? What put the idea into his head? These are questions answered by a French scholar, M. Weil; in one of his ingenious and learned 'Études sur le Drame Antique,' he explains that Horace derived much of his theory of the poetic art from the Alexandrian critics, and more particularly from the writings of a certain Neoptolemus of Parium. Probably the Alexandrian authors of tragedy had been led to adopt a division into five acts by following the example of Euripides, whose practise was not uniform, but who tended to reduce to four the number of the lyric odes in his tragedies, thus separating the purely dramatic passages into five parts.
In Athens the drama had been slowly evolved out of the tragic songs; and in the surviving tragedies of Æschylus, the earliest of the three great dramatic poets of Greece, we discover that the choral odes are more abundant than the dialog which carries on the plot. In the extant plays of his mighty successor, Sophocles, the drama is seen emerging triumphant, but the lyrical passages are still frequent and important. In the later pieces of Euripides, the third and most modern of the Attic tragedians, we note that the drama has almost wholly disengaged itself from the lyric out of which it sprang. In Æschylus and in Sophocles the number of choral odes and the number of episodes, of purely dramatic passages in dialog, is never fixed, varying from play to play as the plot might demand. But in Euripides the choral odes are more detached from the drama; beautiful in themselves, they seem to exist rather for their own sake than in any integral relation to the play itself. And apparently Euripides was far more interested in his play, in his plot, and in his characters, than in these extraneous lyric passages, so he reduced them to the lowest possible number, generally to four, serving, so to speak, as exquisite interact music, separating the pathetic play into five episodes in dialog.