The present work began innocently enough with a small essay correcting Mill's famous and influential misinterpretation of Comte's opposition to “psychology.” As I explain in Chapter 1, what Comte rejects and what Mill defends are two different subjects. Comte's arguments are directed against late incarnations of traditional rational psychology, and his prime target is Cousin's pseudoscientific idea of an “interior observation” that supposedly provides metaphysical knowledge of the soul. Mill criticizes Comte for opposing empirical (sc., associationist) psychology and the “introspection” on which it depends. In fact, Comte never considers either of these topics.

Yet Mill's misinterpretation, once identified, seems so obvious that I began to wonder how he could have made it. Indeed, in researching the psychology controversy, I found several other issues on which Mill misinterprets Comte in equally obvious ways (e.g., by criticizing Comte for never getting around to an “organon of proof,” when Comte in fact opposes the very idea of one). Eventually I saw the larger problem. Mill takes it for granted that, being both “positivists,” he and Comte must be in basic agreement over what this entails. In this, however, Mill – and all of us who have read him rather than Comte – are deeply mistaken. As I explain in Chapter 2, Mill's outlook already resembles our century's Logical Positivism in being both rationally reconstructive and ahistorically oriented.