A tragedy is about human suffering and is not inherently good or evil. Some of the actions of characters in the play may be good or evil, but the play itself is not. In Hamlet, Claudius's actions are certainly evil and Hamlet's inaction ultimately leads to much suffering, but it is not an evil tragedy. Likewise, Oedipus unwittingly causes the death of his father and a plague to fall upon Thebes in Oedipus Rex, but again, it is not an evil tragedy. There is good and evil in both plays. For example, once Oedipus finds out that he is the man responsible for the plague, he exiles himself from the city (as he promised he would do to the perpetrator). This could be seen as a "good" action. Also, Hamlet ultimately avenges his father's death and disposes of a fratricidal king, but he causes a great deal of collateral damage (Ophelia, Polonius, etc.) by his actions and inactions.