Book excerpt: ​The motivation for this volume is simple. For a variety of reasons, clinical psychologists have long shown considerable interest in the philosophy of science. When logical positivism gained currency in the 1930s, psychologists were among the most avid readers of what these philosophers had to say about science. Part of the critique of Skinner’s radical behaviorism and thus behavior therapy was that it relied on, and thus was logically dependent on, the truth of logical positivism—a claim decisively refuted both historically and logically by L.D. Smith (1986) in his important Behaviorism and Logical Positivism: A Reassessment of the Alliance. ​