The psychology of motivation is a broad and loosely defined field. It covers everything from detailed investigations of the physiological mechanisms involved in animal drives to elaborate analyses of the unconscious motives behind abnormal or symptomatic acts in a person to factor analyses of the motives people assign to themselves to explain their behavior. Different textbooks and different courses have been organized around these different areas of investigation. In this book we will draw on all these sources of information and attempt to provide an integrated view of the field by narrowing somewhat the focus of attention.

The book emphasizes how motives differ from other determinants of action and how they relate to other motivation-type variables such as emotions, incentives, values, causal explanations, and conscious and unconscious intents. It examines how motives are acquired, where they come from, and on what they are based. Biological sources of human motives are reviewed, and this review introduces the topic of natural incentives, or what is sometimes called intrinsic motivation. Some selectivity is necessary in reviewing the large field of animal research on motivation in order to focus on biological sources of individual differences in human motive strength. Social sources of differences in motive strength are also considered, including everything from the way parents rear their children to educational interventions designed to change peoples' motives. Such studies contribute not only practical information on how to develop motives, but also theoretical information on the nature of motives and how they differ from other characteristics.