Relation to Søren KierkegaardNietzsche knew little of the 19th-century philosopher Søren Kierkegaard.Angier, Tom P. Either Kierkegaard/or Nietzsche: Moral Philosophy in a New Key. ISBN 0-7546-5474-5 Georg Brandes, a Danish philosopher, wrote to Nietzsche in 1888 asking him to study the works of Kierkegaard, to which Nietzsche replied that he would.
Recent research, however, suggests that Nietzsche was exposed to the works of Kierkegaard through secondary literature. Aside from Brandes, Nietzsche owned and read a copy of Hans Lassen Martensen’s Christliche Ethik (1873) in which Martensen extensively quoted and wrote about Kierkegaard’s individualism in ethics and religion. Nietzsche also read Harald Høffding’s Psychologie in Umrissen auf Grundlage der Erfahrung (ed. 1887) which expounded and critiqued Kierkegaard’s psychology. Thomas Brobjer believes one of the works Nietzsche wrote about Kierkegaard is in Morgenröthe, which was partly written in response to Martensen's work. In one of the passages, Nietzsche wrote: Those moralists, on the other hand, who, following in the footsteps of Socrates, offer the individual a morality of self-control and temperance as a means to his own advantage, as his personal key to happiness, are the exceptions. Brobjer believes Kierkegaard is one of "those moralists".
The first philosophical study comparing Kierkegaard and Nietzsche was published even before Nietzsche's death.Miles, Thomas. Rival Visions of the Best Way of Life in Kierkegaard and Existentialism, Jon Stewart, ed. p.263. More than 60 articles and 15 full-length studies have been published devoted entirely in comparing these two thinkers.