"The main task of this book is to analyze the application of motivational concepts in contemporary behavior theory" (p 142). This analysis is done in four steps which arbitrarily represent four parts of the book. Step one is a brief and useful introduction to the philosophy of science. This is done in order to highlight what is entailed in an explanation of behavior. The second step (chapters 2 to 5) presents a historical perspective from which the author views later theoretical formulations. In this historical survey the contributions of Freud to motivational theory are properly acknowledged. What is refreshing in this survey is that Freud is seen as one of many, and not the only, motivational theorist. The third step (chapters 6 to 11) analyzes Hull's theory of motivation, especially the drive construct and the various properties it is to have. The last part of Bolles'