With unusual liveliness in style, Quine measures both logical practice and theory against language as well as conditions of philosophical precision. Thus, he builds the full predicate calculus through sentence and first-order quantifier logic, always in touch with colloquial language. The fourth part of the book, which also offers insights into set theory and foundational problems of mathematics, deals with identity logic, singular terms, and designators, and "sharpens the old ontological knife.".