Book Review: Not Exactly: In Praise of Vagueness by Kees van Deemter

Politicians and salesmen aren’t the only people who use — or even rely on — vague language. Never mind that much of the world can be measured in neatly defined units such as centimeters, milligrams and degrees, writes van Deemter, a computer scientist. Most people have little sense of those units, so vagueness permeates speech and ideas, from describing a person as “tall” to the weather as “chilly.”

Van Deemter argues that vagueness is not only the norm, but can even be useful. The imprecision of “chilly,” for example, quickly conveys a comparison and judgment that isn’t necessarily captured by a precise temperature reading.

Much of the book surveys vagueness in unexpected places, like mathematics and the study of logic. Chapters explore the sorites paradox (which concerns the question of how many stones make a heap) and physicists’ quest to define the meter in increasingly precise terms. But forget eliminating imprecision, van Deemter contends. Like original sin, he writes, vagueness is “a stain that can be diminished but never removed.”

Besides being inevitable, vagueness can be essential. Engineers developing artificial intelligence, for example, know the importance of building in fuzzy logic.  “If we were to build a robot that can communicate, how precise would we like it to be when it speaks to us?” asks van Deemter. Such questions are intriguing, though at times the book’s philosophical wanderings become overly complex. The author makes a strong central argument, though: In a world of shades of gray, vagueness can be a virtue.

Oxford Univ. Press, 2010, 341 p., $29.95.