There is no greater thinker of decadence than Friedrich Nietzsche. This is how Nietzsche defines decadence in The Case of Wagner as a “question of style”:
“I dwell this time only on the question of style–What is the sign of every literary decadence? That life no longer dwells in the whole. Word becomes sovereign and leaps out of the sentence, the sentence reaches out and obscures the meaning of the page, the page gains life at the expense of the whole–the whole is no longer a whole. But this is the simile of every style of decadence: every time, the anarchy of atoms, the disgregation of the will, “freedom of the individual,” to use moral terms–expanded into a political theory, “equal rights for all.” Life, equal vitality, the vibration and exuberance of life pushed back into the smallest forms; the rest, poor in life. Everywhere paralysis, hardship, torpidity, or hostility, and chaos: both more and more obvious the higher one ascends in forms of organization. The whole no longer lives at all: it is composite, calculated, artificial, and artifact.”
As Andrew Huddleston has recently written, Nietzsche understands that “decadence is literally a kind of disorder – that is, a lack of cohesive order – within the individual or the culture.” It is a sickness by which individuals and groups think only of themselves and lose sight of their belonging to a common world or a meaningful order.