Existentialism is not easily definable. Its protagonists have traced it back to Pascal, to St. Augustine, even to Socrates. It has been alleged in our time to be the doctrine of writers as various as Miguel de Unamuno and Norman Mailer. At first sight, characteristics of the doctrine are almost as various. That two writers both claim to be existentialists does not seem to entail their agreement on any one cardinal point. Consequently, to define existentialism by means of a set of philosophical formulas could be very misleading. Any formula sufficiently broad to embrace all the major existentialist tendencies would necessarily be so general and so vague as to be vacuous, for if we refer to a common emphasis upon, for example, the concreteness of individual human existence, we shall discover that in the case of different philosophers this emphasis is placed in contexts so dissimilar that it...