Thanks to the Greeks, we can distinguish tragedy from comedy in drama, and so we still tend to assume that each is the half of drama that is not the other half. When we come to deal with such forms as the masque, opera, movie, ballet, puppet-play, mystery-play, morality, commedia dell’ arte, and Zauberspiel, we find ourselves in the position of the Renaissance doctors who refuse to treat syphilis because Galen said nothing about it.

— Northrup Frye, Anatomy of Criticism