As in many areas of psychology, there are close linkages between the Humanistic Approach and philosophy. For example, Rogers's concept of the phenomenal field as the basis of defining the self can be linked to the ideas of phenomenological philosophers like Edmund Husserl. Similarly, the existentialist tradition began with European philosophers like Soren Kierkegaard and Jean-Paul Sartre. While its roots extend back to the turn of the 20th century (and some would say even earlier), it really gained momentum as a result of World War II, whose devastation and destruction gave a sense of immediacy to questions about the purpose of living. (For example, Albert Camus, a leading existentialist writer, was a member of the French Resistance.) Existentialists start from the premise that there is no absolute meaning to life, and hence that life in a purely rational sense is without purpose. Interestingly, however, from this bleak beginning, many arrive at interpretations that nonetheless affirm a value to life.