Influencing philosophers such as Sartre and Camus, and still strikingly modern in its psychological insights, Kierkegaard's The Sickness Unto Death explores the concept of 'despair' as a symptom of the human condition and describes man's struggle to fill the spiritual void.

Throughout history, some books have changed the world. They have transformed the way we see ourselves - and each other. They have inspired debate, dissent, war and revolution. They have enlightened, outraged, provoked and comforted. They have enriched lives - and destroyed them. Now Penguin brings you the works of the great thinkers, pioneers, radicals and visionaries whose ideas shook civilization and helped make us who we are.