IN RECENT years there has been a noteworthy development of methods for measuring many of the objective factors which are associated with the existence of markets. Studies of the distribution of population, of incomes, of trading areas, of retail outlets, have multiplied. New methods of approach have been devised and new sources explored. Data which would have been unobtainable twenty-five years ago are now widely available. Knowledge of the subjective factors, which also profoundly influence the marketability of products, has on the other hand failed to show comparable progress. Whether this lack of development is due to the complexity of the subject, or to the preoccupation of students of marketing with other affairs, the fact remains that relatively little is known of the mental processes of the people who buy goods. Isolated studies of consumers' wants, interests, prejudices and attitudes have indeed been made, but the general stock of information on these and similar points remains sadly inadequate. Without such information the picture of the market is like a jigsaw puzzle with important parts missing. On the side of theory, ideas concerning consumers' mental activities are in a primitive state. Most textbooks on marketing include a few general remarks on the subject, accompanied by an arbitrary list of the buying motives which are supposed to lead to the purchase of goods and services. Such lists, even if their validity is granted, are somewhat like the lists of bones of the body which formerly appeared in textbooks of physiology; they are interesting as illustrations of the atomic theory applied to human nature, but they fall far short of explaining the activities of the living mechanism.