A few days after finalizing the chapters of this book, I happened to watch a television documentary about string theory, one of the latest approaches by which physicists are pursuing a unified theory of nature. By conceiving subatomic particles as loops or pieces of string, instead of dimensionless points or spherically symmetric fields of force, the program explained, physicists have found new possibilities for mathematically connecting nature's forces. Some think the long sought-for unification of general relativity and quantum mechanics may soon come into view.

For one who had just written a book about the Unity of Science movement of the 1930s and '40s, this documentary brimmed with significance. Were they alive today and sitting in front of my television with me, I realized, the philosophers who led this movement – Otto Neurath, Rudolf Carnap, Philipp Frank, and Charles Morris – would have been fascinated. The science would have impressed them, but so would the efforts of public television to popularize contemporary physics and its unificationist impulse. Their Unity of Science movement was, in part, an effort to do just that.

On the other hand, these philosophers might well be disappointed were they to come back to life. For unlike public television, the discipline of philosophy of science they helped to cultivate in North America no longer holds the unity of science among its core issues and concerns. Especially during the postmodern 1980s and '90s, after all, one of the more celebrated concepts in the humanities was disunity.