"At the heart of The Birth of Tragedy lies the opposition between the two Greek gods, Apollo and Dionysus, who in turn stand for two antagonistic aesthetic principles that are nonetheless complementary and equally vital to the production of the highest art. Apollo and his abstraction the Apollonian represent the realm of clear and luminous appearances, plastic images, dreams, harmless deception... while Dionysus and the Dionysian represent hidden metaphysical depths, disturbing realities, intoxication, and traits that are typically exotic and unclassical (ecstasy, disorderliness, dance, orgy). The history of Greek art is the history of the relation between these two principles."
James I. Porter, The Invention of Dionysus