When I wrote the first edition of Motivation (1978) , my goal was to provide an empirically based introduction to a broad range of motivational theories and principles. The phenomena described ranged from homeostatic motives in animals to motives for human social interactions. Many theoretical viewpoints were covered, as they should be in a text, but my own predilection was for hedonic theory with a liberal sprinkling of learning theory. This was explicitly stated and the concepts of desire and aversion were considered the most fundamental concepts in the book. About that same time, research on emotion rapidly began to expand, and in the second (1983) and subsequent editions a chapter on emotion was added. This fifth edition of Motivation: Theories and Principles expresses the same orientation as that found in earlier editions. It is an experimentally oriented survey of research and theory on animal and human an motivation, emphasizing hedonic principles.
In the first edition I noted that it is difficult to maintain a completely logical and consistent conceptualization of motivation without sacrificing a large amount of material that many people consider important to the topic. This is still true. Motivation theorists and researchers are still fragmented in their efforts to understand motivation. Much of the reason for this, it still seems to me, is that evolution has not been a logical and consistent process. Consequently, theoretical principles developed in the context of one species or motivational problem, say eating behavior in omnivores (like humans and rats), may not be applicable to a different set of motivational problems or to the same problems in different species (such as eating in herbivores or carnivores). The end result is a great diversity of approaches to motivation, none of which is the correct approach but all of which have their own strengths. For reasons such as this, the first chapter is still devoted to discussion of the nature of scientific theory, just so the student can gain greater insight as to what theories and theorizing are all about, and why they are essential.
Given the same ambitions as before, there are similarities with the previous editions as well as differences. One of these similarities is the attempt to weave an historical perspective into as many topics as reasonable in a limited space. Some older concepts and theories may not be as important as they once seemed (such as drive theory) but such concepts have a way of reappearing, sometimes under new names. The strengths and weaknesses of the earlier concepts may apply to the new concepts, and it seems to me there is much to be gained by at least familiarizing students with some of the older concepts. Reflecting recent scholarship, however, there are numerous changes in content and references for this edition.
