Although their final acts couldn't be any more dissimilar, classic tragedies and comedies share a wide range of similarities. In fact, other than the difference in the hero's fate at the end, well structured comedies and tragedies are built around the same basic principles, as both use intimate looks at characters to extrapolate themes about the world in which they are set.
Both tragedies and comedies hinge upon their characters and their characters' personal development over the course of the play. Like modern fiction, there isn't much of a story in a play unless one of the characters undergoes a significant change in outlook or personal growth as part of the conflict. In most cases, this character development isn't independently triggered by events unfolding in the plot, but is a central catalyst to the story. Situations create self-awareness in characters, who apply their new outlook to their lives, further driving conflict or forcing change. In "Romeo and Juliet" and "A Midsummer Night's Dream," both Juliet and Hermia's awareness of love against proscribed social bonds is created, and then drives each play.
Morally Flawed Characters
Although the Greeks introduced the notion of the tragic flaw into their characters, Renaissance writers refined the idea. No longer was a flaw limited to epic heroes and laid the grounds for their undoing, but a symptom present in almost all common men. These moral flaws are either tested against societal rules, as Romeo and Juliet's love and commitment is tested by the feud between their families, or society exposes the moral flaw in a character driving the story, such as in Voltaire's "Tartuffe," which centers on the titular characters' moral shortcomings and hypocrisy.
Examination of Social Issues
While the draw of a tragedy or comedy is the power that their highly emotionally identifiable characters bring to the stage, comedies and tragedies use people to expose societal issues. Whether it's by showing the emotional turmoil caused by social pressures or by plotting the undoing of social norms, social issues provide the foundation for every comedy and tragedy. Euripides' "Medea" explores the role of women in Greek society, Shakespeare's "Hamlet" centers around the machinations of a royal court and "A Raisin in the Sun" confronts de facto racism in America in the middle of the 20th century.