Tragedies are stories in which a sympathetic character arouses the affections of the audience, then is beleaguered by bad fortune or a downfall of some sort. While tragedy tends to be a "serious" genre (running strongly to the dramatic), a too-serious approach can come across as heavy-handed. Comedy, used in this sense as a broad-based term for mirth, amusement and good fortunes, can be used to lighten a mood, relieve tension in tragic stories and even illuminate the tragic storyline by providing a counterpoint to it.
Tragedies illuminate fatal flaws in a character or in the world itself, and conflicts typically are resolved only upon the death of the hero or the ultimate demise of the subject of the work. Comedies, in which everyone ultimately forgives, forgets or moves on in a reversal of fortune, are intrinsically different, but comedic elements can nevertheless be used to complement the elements of the tragic tale. For example, tragic heroes expect far too much from life and always fail, usually because of forces attributed to the world itself. To avoid the dull platitudes of a Godlike character, comedic elements (such as small moments of self-inflicted bad luck) can lighten the load and endear the character to the audience.
Aristotle, according to DePaul University's David Simpson, credits the origin of comedy to the ancient Greek concept of "komos," in which a sympathetic character is on the receiving end of good fortunes. Aristotelian tragedy, the opposite of comedy, usually dealt with death, destruction or the downfall of a once-great hero, inspiring pity for the character and fear from the audience.
In the collective consciousness, tragedies are often thought of as "having a sad ending," while comedies have "happy" endings. While this might be the case in many cases, such a definition illustrates an oversimplification. The defining characteristics of classic comedies and tragedies include the traits of their heroes--infallible heroes who are defeated, or hapless sprites who overcome--as much as their conclusions.
Shakespeare was a master of blending tragic stories with comedic elements in order to resonate with his audience and relieve dramatic tension. For instance, "Romeo and Juliet," one of the great tragedies of literature, is replete with comedy, from Juliet's nun nurse to Romeo's motley crew of friends. Shakespeare uses them to make "Romeo and Juliet" much more than a routine tragedy.