Søren Kierkegaard published *Enten – Eller* in Copenhagen in February 1843, under the pseudonym Victor Eremita. The fictional editor presents two sets of papers he claims to have found in a second-hand secretary: 'A's papers' — the essays of an aesthetic young man — and 'B's letters' — the long letters of an ethical man, a judge, addressing the young man on his way of life. The book is therefore read not as a philosophical thesis but as two ways of life speaking in two voices.

A's sections include a philosophy of music on 'Don Giovanni', the 'Diary of a Seducer' (a cool manuscript on the art of seducing a young woman), and the 'Diapsalmata' aphorisms. Life is reduced to the aesthetic moment: there is no meaning, only the avoidance of boredom. B's letters criticise this directly: the aesthetic life is in fact despair, because it never constitutes a 'self'; everything is contingent on external stimulus. The ethical life B proposes — marriage, vocation, responsibility, choice — is the constitution of a self.

Kierkegaard's central move is this: it cannot be proved which life is 'the right one'; the choice between them is not made by logic but by passion. Logic is only a way of inspecting a life; living — really living — is a decision. Hegel's system hides this leap; Kierkegaard places it in front of us. 'Subjectivity is truth', he will later say: the truth of a life follows not from objective proofs but from how the person lives it.

The book was little read outside Denmark until the twentieth century. When Heidegger, Jaspers, and Sartre began reading Kierkegaard in the 1920s, they realised half of their own existentialist programme had already been laid out by him.