Søren Kierkegaard's The Concept of Anxiety and The Sickness Unto Death were published in the 1840s. The discussion of freedom and anxiety in these works laid the foundation for existentialism. Kierkegaard was the first modern philosopher and the first person to find himself in a modern age. However, his faith and spirituality make him timeless.
Philosophy departments consider The Concept of Anxiety and The Sickness Unto Death to be a pair.
The Concept of Anxiety explores sin, guilt, and anxiety, which is undirected fear, a general sense of dread. Kierkegaard rebuffs the idea that anxiety is caused by original sin. Rather, innocence generates the conditions for anxiety. Consider Adam and Eve in the Garden of Eden; recall that God forbade Adam from eating from the tree of knowledge. God's directive makes Adam aware that he has a choice. This freedom to choose causes anxiety. Furthermore, Adam could not have known he was sinning because, being the first to sin, how would he know what sin was? Sin was real only after Adam ate from the tree of knowledge. Rejoice in your freedom.
The Sickness Unto Death explores spiritual death, which is despair. Here, Kierkegaard deals with self, or the self-concept of selfhood: the "relation's relating itself to itself in the relation." In The Sickness Unto Death, Kierkegaard delves into the binary concepts of the finite and the infinite and the possible and the necessary. Tension between these polarities results from not being right with God. And, thus, despair. Kierkegaard elaborates further that there are three kinds of despair. All this is not as interesting as The Concept of Anxiety, so I will not elaborate. However, my favorite passage in The Sickness Unto Death comes when Kierkegaard is describing the person who lives life in a religious mode, but who, in the process of becoming spiritual, has lost his self:
Such things do not create much of a stir in the world, for a self is the last thing the world cares about and the most dangerous thing of all for a person to show signs of having. The greatest hazard of all, losing the self, can occur very quietly in the world, as if it were nothing at all. No other loss can occur so quietly; any other loss--an arm, a leg, five dollars, a wife, etc.--is sure to be noticed.
