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 alreadyIn chapter 6. 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.