The title of [What Is Existentialism?] would lead one to expect a pedestrian but systematic introduction to the subject of the sort usually addressed in the preface "to the general reader" or to "the educated public"—but which normally mystifies and rarely educates. Happily, the title is deceptive. This volume is neither a systematic treatment nor one which deals with existentialism in general. It offers instead two essays, related and partly overlapping, on the thought of one philosopher, Martin Heidegger. Moreover, these two essays, the composition of which was separated by "more than a dozen years," represent the author's attempt, not to popularize, but to divine the significance of Heidegger's thought as an event in the history of philosophy.

But in the end Mr. Barrett's accomplishment of this task does constitute, in a way, a highly successful introduction to existentialism; indeed, this is one of the best secondary...