Aristotle now narrows his focus to examine tragedy exclusively. In order to do so, he provides a definition of tragedy that we can break up into seven parts: (1) it involves mimesis; (2) it is serious; (3) the action is complete and with magnitude; (4) it is made up of language with the "pleasurable accessories" of rhythm and harmony; (5) these "pleasurable accessories" are not used uniformly throughout, but are introduced in separate parts of the work, so that, for instance, some bits are spoken in verse and other bits are sung; (6) it is performed rather than narrated; and (7) it arouses the emotions of pity and fear and accomplishes a katharsis (purification or purgation) of these emotions.
Next, Aristotle asserts that any tragedy can be divided into six component parts, and that every tragedy is made up of these six parts with nothing else besides. There is (a) the spectacle, which is the overall visual appearance of the stage and the actors. The means of imitation (language, rhythm, and harmony) can be divided into (b) melody, and (c) diction, which has to do with the composition of the verses. The agents of the action can be understood in terms of (d) character and (e) thought. Thought seems to denote the intellectual qualities of an agent while character seems to denote the moral qualities of an agent. Finally, there is (f) the plot, or mythos, which is the combination of incidents and actions in the story.
Aristotle argues that, among these six, the plot is the most important. The characters serve to advance the action of the story, not vice versa. The ends we pursue in life, our happiness and our misery, all take the form of action. That is, according to Aristotle, happiness consists in a certain kind of activity rather than in a certain quality of character. Diction and thought are also less significant than plot: a series of well-written speeches have nothing like the force of a well-structured tragedy. Further, Aristotle suggests, the most powerful elements in a tragedy, the peripeteia and the anagnorisis, are elements of the plot. Lastly, Aristotle notes that forming a solid plot is far more difficult than creating good characters or diction.
Having asserted that the plot is the most important of the six parts of tragedy, he ranks the remainder as follows, from most important to least: character, thought, diction, melody, and spectacle. Character reveals the individual motivations of the characters in the play, what they want or don't want, and how they react to certain situations, and this is more important to Aristotle than thought, which deals on a more universal level with reasoning and general truths. Melody and spectacle are simply pleasurable accessories, but melody is more important to the tragedy than spectacle: a pretty spectacle can be arranged without a play, and usually matters of set and costume aren't the occupation of the poet anyway.
Aristotle's definition of tragedy at the beginning of this chapter is supposed to summarize what he has already said, but it is the first mention of the katharsis. The Greek word katharsis was usually used either by doctors to talk about purgation, the flushing of contaminants out of the system, or by priests to talk about religious purification. In either case, it seems to refer to a therapeutic process whereby the body or mind expels contaminants and becomes clean and healthy. Determining exactly what role katharsis is meant to play in tragedy is somewhat more difficult.
First, we might ask what exactly katharsis is in reference to tragedy. The idea, it seems, is that watching a tragedy arouses the emotions of pity and fear in us and then purges these emotions. But, by virtue of mimesis, we aren't feeling real pity or real fear. I may feel pity for Oedipus when he learns that he has killed his father and married his mother, but this is a different kind of pity than the pity I feel for the homeless or for those living in war zones. I know that Oedipus is not a real person and that no one is really suffering when I watch Oedipus suffer. As a result, I can empathize with the character of Oedipus without feeling any kind of guilt or obligation to help him out. Watching tragedy has a cathartic effect because I can let go of the emotional tension built up in me as I leave the theater. I am able to experience profound emotion without having its consequences stay with me and harden me to subsequent emotional shocks.