The Poetics of Aristotle

[The parts of Tragedy which must be treated as elements of the whole have been already mentioned.  We now come to the quantitative parts, and the separate parts into which Tragedy is divided, namely, Prologue, Episode, Exode, Choric song; this last being divided into Parode and Stasimon.  These are common to all plays:  peculiar to some are the songs of actors from the stage and the Commoi.

The Prologue is that entire part of a tragedy which precedes the Parode of the Chorus.  The Episode is that entire part of a tragedy which is between complete choric songs.  The Exode is that entire part of a tragedy which has no choric song after it.  Of the Choric part the Parode is the first undivided utterance of the Chorus:  the Stasimon is a Choric ode without anapaests or trochaic tetrameters:  the Commos is a joint lamentation of Chorus and actors.  The parts of Tragedy which must be treated as elements of the whole have been already mentioned.  The quantitative parts the separate parts into which it is divided—­are here enumerated.]