The Philosophical Forerunners
Existential psychology has always maintained a close relationship with existential philosophy. The interaction between these two disciplines and their common bond of existentialism has been mutually beneficial. Because of this, it can be very helpful to know some about the existential philosophers.
Nietzsche
Nietzsche is an often misunderstood existentialist. Much of the confusion comes from the change which occurred in his thought over time. His thought could be divided into three stages. In the first stage, Nietzsche was heavily influenced by his mentors, including Richard Wagner. The second stage was his most prolific and important writing. It was during this period that he developed independence as a writer and a thinker; often being very critical of his previous mentors. The final stage of thought came toward the end of his life when he was struggling with a disease which many believed influenced his thought in a detrimental manner. It was during this time that he wrote one of his most famous books, The Will to Power. However, many Nietzsche experts, including Walter Kaufmann (1974), do not believe this is very representative of his overall thought. Many of these experts point to Thus Zarathustra Spoke as his seminal work.
Nietzsche has also be misunderstood due to his relation to the Nazi party and religion. Hitler used many of Nietzsche's later writings out of context to support many of his ideologies and his racism. In reality, Nietzsche was an early critique of the Nazi party long before Hitler came into power (Kaufmann, 1974). In general, Nietzsche's thought stands in strong opposition to the ways in which it was used by Hitler and his followers.
Nietzsche's criticism of religion offended many and created many strong critiques of his writing. However, much of Nietzsche's statements on religion are also misunderstood. He was not so much anti-religion as he was anti-dogmatic or fundamentalist religion. Yet few people see past his famous statement "God is dead" to hear some of his valid and important critiques of dogmatic religion.
Many very important contributions to existential thought emerged from Nietzsche's writings. In honor of this, some consider him to be the first true existentialist. However, it is more common to give that honor to the next philosopher to be discussed: Kierkegaard.
Soren Kierkegaard
Kierkegaard was a Christian theologian and philosopher who was acutely interested in the human condition. Of particular importance, Kierkegaard wrote was is generally considered the first psychological essay on anxiety in his book The Concept of Anxiety (1981; also sometimes translated as The Concept of Dread.). Kierkegaard also wrote a very early developmental view of morality and religious belief.
Consistent with the other early existential philosophers, Kierkegaard valued critical thought and honesty about the human condition. His brutal honesty about the human condition in all its glory and all its shame was difficult for many of his readers. It has often attributed to what many describe as a life long struggle with depression. As the father of existentialism, Kierkegaard has been profoundly influential on existential theology, existential philosophy, and existential psychology.
Jean-Paul Sartre
Though generally not considered the first existential philosopher, Sartre was the person who first coined the term "existential." His most influential work, Being and Nothingness (1956), remains an existential class. The common perceptions of Sartre are of his writings being rather cynical, dark, and obtuse. While Sartre is not one of the more optimistic existentialists, his writings are often painted in an unfairly negative light. Another important influence of Sartre is in helping establish much of the common terminology of existential theory.
Heidegger
Heidegger is generally grouped more as a phenomenologist than as an existentialist; however, his thought has been very influential on the development of existential thought. His most important contribution, Being and Time, continues to be a commonly cited reference in existential literature. Heidegger's contributions is one of the primary reasons why existential and phenomenological thought often get lumped together.
Original Version added 2004. Never been updated.