and it is actions such as these which, according to our hypothesis, tragedy represents; and, moreover, misfortune and good fortune are likely to turn upon such incidents.
Now since the discovery is somebody's discovery, in some scenes one character only is discovered to another, the identity of the other being obvious; but sometimes each must discover the other. Thus Iphigeneia was discovered to Orestes through the sending of the letter, but a separate discovery was needed to make him known to Iphigeneia. [Note]
We see then that two elements of the plot, reversal and discovery, turn upon these incidents. A third element is a calamity. Of these three elements we have already described reversal and discovery.
A calamity is a destructive or painful occurrence, such as a death on the stage, acute suffering and wounding and so on.
We have already [Note] spoken of the constituent parts to be used as ingredients of tragedy. The separable members into which it is quantitatively divided are these: Prologue, Episode, Exode, Choral Song,
the last being divided into Parode and Stasimon.
These are common to all tragedies; songs sung by actors on the stage and "commoi" are peculiar to certain plays.
A prologue is the whole of that part of a tragedy which precedes the entrance of the chorus.