The idea of decadence presents many variants of which two alone have a truly decisive importance. One is the biological, physiological and psychological variant; the other, the literary, esthetic and spiritual variant. The latter is so much more significant than the former that it often incarnates the very constant of the idea of decadence. This constant is eminently historical: everyone knows that when decadence, and nothing else, is being spoken about, it is not so much the degeneration of the species or of an individual that is under consideration, as the decline of a social and political organism or, more generally, of a society or a civilization. All modern speculation with regard to the notion of decadence derives from this principle.