Fear and Trembling + The Sickness Unto Death by Soren Kierkegaard

Kierkegaard counted tHess among "the most perfect books I have written," and in them he introduces two terms--"the absurd" and "despair"--that have become key terms in modern thought.

Fear and Trembling takes up the story of Abraham and Isaac while The Sickness Unto Death examines the spiritual anxiety of despair.

Fear and Trembling and The Sickness Unto Death established Kierkegaard as the father of existentialism.