THE AGE OF REASON (397 pp.)Jean-Paul Sartretranslated by Eric Sutton Knopf ($3).
What is existentialism? As far as most Americans are concerned, it is the latest incomprehensible fashion from France. U.S. audiences now have a thorough chance to sample the brew that has been boiling furiously in Europe's intellectual teapots. The pontiff and leading practitioner of existentialism is France's stubby (5 ft.), scholarly Jean-Paul Sartre. His Age of Reason is a dolorous, idea-clotted novel full of moldy characters and philosophic yawpings about life. It is sure to win its author some critical praise....