Aristotle approaches poetry with the same scientific method with which he treats physics and biology. He begins by collecting and categorizing all the data available to him and then he draws certain conclusions and advances certain theses in accordance with his analysis. In the case of tragedy, this means he divides it into six parts, identifies plot as the most important part, and examines the different elements of plot and character that seem to characterize successful tragedies. He tentatively suggests that tragedy ultimately aims at the arousal of pity and fear and at the katharsis of these emotions. Then he begins to lay out certain theories as to what makes a good tragedy: it must focus on a certain type of hero who must follow a certain trajectory within a plot that is tightly unified, etc. Aristotle's conclusions, then, are based less on personal taste and more on an observation of what tends to produce the most powerful effects.
Aristotle's method raises the fundamental question of whether poetry can be studied in the same way as the natural sciences. Though there are some benefits to Aristotle's method, the ultimate answer seems to be "no." The scientific method relies on the assumption that there are certain regularities or laws that govern the behavior of the phenomena being investigated. This method has been particularly successful in the physical sciences: Isaac Newton, for example, managed to reduce all mechanical behavior to three simple laws. However, art does not seem to be governed by unchanging, unquestionable laws in the same way that nature is. Art often thrives and progresses by questioning the assumptions or laws that a previous generation has accepted. While Aristotle insisted on the primacy and unity of plot, Samuel Beckett has achieved fame as one of this century's greatest playwrights by constructing plays that arguably have no plot at all. Closer to Aristotle's time, Euripides often violated the Aristotelian principles of structure and balance in a conscious effort to depict a universe that is neither structured nor balanced. Not surprisingly, Aristotle seems to have preferred Sophocles to Euripides.
These remarks on Sophocles and Euripides bring us to another problem of interpreting Aristotle: we have a very limited stock of Greek tragedies against which to test Aristotle's theories. Aristotle could have been familiar with hundreds, or even thousands, of tragedies. All we have today are thirty-three plays by three tragedians. As a result, it is difficult to say to what extent most tragedies fit Aristotle's observations. Those that we have, however, often grossly violate Aristotle's requirement. The best example we have of an Aristotelian tragedy is Oedipus Rex, so it is no wonder that Aristotle makes such frequent reference to it in his examples.
Three points stand out as probably the most important in the Poetics: (1) the interpretation of poetry as mimesis, (2) the insistence on the primacy and unity of mythos, or plot, and (3) the view that tragedy serves to arouse the emotions of pity and fear and then to effect a katharsis of these emotions. (1) is discussed in the commentary on Chapters 1–3, (2)is discussed in the commentary on Chapter 6 and Chapters 7–9, and (3) is discussed in the commentary on Chapter 6 as well.