Friedrich Nietzsche
The roots of existential psychotherapy lie in philosophy from the 1800s, and more importantly with philosophers whose work dealt with human existence. The philosophers most commonly associated with existential therapy are Søren Kierkegaard and Friedrich Nietzsche. While the two influential thinkers were in conflict regarding the predominant ideologies of their time, they were committed to the exploration of reality and how it was experienced.
Kierkegaard theorized that human discontent could only be overcome via internal wisdom, while Nietzsche introduced the idea of free will and personal responsibility. By the 1900s philosophers like Sartre and Heidegger had begun exploring the role interpretation and investigation had in the healing process.
Over the next few decades other contemporaries began to acknowledge the importance of ‘experiencing’ in terms of achieving psychological well-being.
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Psychotherapeutic Applications of Philosophy 