Peter Unger's provocative new book poses a serious challenge to contemporary analytic philosophy, arguing that to its detriment it focuses the predominance of its energy on "empty ideas."

In the mid-twentieth century, philosophers generally agreed that, by contrast with science, philosophy should offer no substantial thoughts about the general nature of concrete reality. Leading philosophers were concerned with little more than the semantics of ordinary words. For example: Our word "perceives" differs from our word "believes" in that the first word is used more strictly than the second....