Aristotle's Definition of Tragedy.

Aristotle said that tragedy has six main elements; plot, character, thought, diction, melody, and spectacle. Aristotle felt that the action of the play (its plot) was the most important of the six elements. He said, "All human happiness or misery takes the form of action....Character gives us qualities, but it is in our actions--what we do--that we are happy or miserable." There must be Unity of Plot. Any events or episodes must be necessary …

…composes lines that say something extremely well. In a good play, some lines are so well constructed that the audience can leave the play quoting the lines exactly. Melody and Spectacle are accessories. The Greeks sometimes used musical accompaniment. Aristotle said the music (melody) has to blend in with the play appropriately. Spectacle refers to the staging of the play. Again, as with melody, the spectacle should be appropriate to the theme of the play.