The world is nothing but variety and dissimilarity.

—Montaigne

When the Berlin Wall still stood, and Germany was divided, I had trouble remembering which Germany was which. Was the “Federal Republic of Germany” the Communist part, or was that the “German Democratic Republic”? At last I realized the answer: the place that has to call itself democratic isn’t. Now consider: we have one discipline called physics and another called “political science.” Which is the science?

The philosopher Stephen Toulmin, for many years my colleague at Northwestern University, ascribed bogus claims of scientific status not only to a thirst for prestige but also to a mistaken view of knowledge. Since the seventeenth century, philosophers and educated laymen have presumed that true knowledge resembles Euclidian geometry. Newtonian physics, which reduced the amazingly complex motions of the planets to four simple laws, served as a model for all knowledge. And so in the nineteenth century, Auguste Comte, who coined the term “sociology,” originally proposed to call his new discipline “social physics.” In our time, economics downgraded the study of mere historical facts in favor of timeless mathematical models. The humanities as well as the “social sciences” suffer from “physics envy.”

Toulmin spent his career combatting such fallacies, which he found not only philosophically mistaken but also socially destructive. Abstract rationality, he argued, is only one model of knowledge, appropriate in some circumstances but not in others. He once told me about a lecture he attended at