J. In the following few days Nietzsche sent short writings—known as the Wahnbriefe ("Madness Letters")—to a number of friends (including Cosima Wagner and Jacob Burckhardt). Now with the new style of Zarathustra his work became even more alienating and the market received it only to the degree required by politeness.
Nietzsche's key ideas include the "death of God" the Übermensch the eternal recurrence the Apollonian and Dionysian dichotomy perspectivism and the will to power. His sister Elisabeth Förster-Nietzsche acted as curator and editor of Nietzsche's manuscripts during his illness. .