A fine survey--if you happen to be a logical positivist, if you happen to think that philosophy is an analytic microscope (never a speculative telescope), if you happen to agree with Sir Alfred that nothing much of philosophical interest takes place outside of Oxford, Cambridge, Harvard, and the Vienna Circle. If you happen not to be a hard-boiled empiricist in the Humean tradition, however, you may have some objections to Ayer's closely reasoned and, in its dessicated way, highly impressive book. What kind of historical overview of our age, you may wonder, could completely ignore Marx, Durkheim, Freud, Bergson, Dewey, Ortega, Camus, etc.? How could Ayer devote three times as much space to C, I. Lewis as to Heidegger (whom he accuses of ""charlatanism"") and Sartre combined? The answer, to paraphrase Dr. Johnson, is prejudice, pure prejudice. When he doesn't simply pass them over in silence, Ayer puts down schools of thought he dislikes with mild Socratic irony: ""Existentialism,"" he notes disingenuously, ""acquired its name from the tenet that existence is prior to essence, a proposition not easy to interpret but one that might amount to no more than the innocent claim that a thing can not have properties unless it exists."" In expounding the work of more congenial thinkers, from Bertrand Russell and G. E. Moore to W. V. Quine and Hilary Putnam, Ayer is clear, acute, and a formidable debater. Unfortunately, this forensic talent is turned against his own subjects, so that he constantly attacks and corrects them or even supplies what they should have said. (E.g., after Moore showed that the notion of goodness did hot represent any natural quality, he ought to have concluded that ""'good,' hot being a descriptive term, did hot stand for any quality at ail."" Poor fellow!) Professional philosophers may relish Ayer's disputatious commentary, but readers who suspect that much of 20th-century philosophy is a jejune academic exercise will find their suspicions amply confirmed here.