I reading about Aristotle poetics,

http://classics.mit.edu/Aristotle/poetics.html

http://www.english.hawaii.edu/criticalink/aristotle/index.html

http://www.sparknotes.com/philosophy/aristotle/section11.rhtml

http://www.amazon.com/Aristotles-Poetics-Dramabook-Aristotle/dp/0809005271

http://www.stenudd.com/aristotle/aristotle-poetics.htm

http://www.iep.utm.edu/aris-poe/