Originally published in 1973, this book examines the difficulties which sociologists have in providing useful scientific definitions of terms like 'prejudice' and 'discrimination'. The author argues that such notions are essentially dependent on the social policy adopted, and that their common misuse by sociologists reflects a deeper confusion - that between the sociologist's search for social rules and regularities, and their search for social laws. The book clarifies the complex and important relationships between a scientific interest in the rule-oriented behaviour of people and a scientific interest in social laws about that behaviour. It explains how and why so many sociological inquiries lead to the discovery of mere social practices rather than social laws.