We have posed and answered this question for successive undergraduate and graduate classes. Students have usually expected an authoritative answer, but while giving answers, we have also been led to a continuing inquiry about the essential characteristics of this field. Established disciplines and professions have less need to seek for their identity. Natural sciences find their logic in their empirically supported theories. Some social sciences, having existed for a century or more, can draw on observers' familiarity with them to gain tolerance of their internal heterogeneity or their inadequate bridges to one another.
Most professions rest their claims to authority on service and the expertise to provide it.
These justifications, if we can find them, can not only characterize the field for students and onlookers but also guide its internal development. It is establishing itself and defining its realm of competence. Increasing efforts are being made, however, to consider more explicitly how the field should be defined. In this task we must go beyond classifying the current practices of policy schools and analysts to consider further activities that might be included. This book proposes a basis for organizing graduate education in the field, in terms of experts' justifiable roles in aiding policy choice in a democratic polity.