The narrowest sense of "critical theory" applies to a group of people affiliated with the Institut für Sozialforschung (Institute for Social Research), in Frankfurt, German. In general, the Institute has been concerned with some of the same problems that interested German idealism of the 19th century - the nature of truth, reason, beauty, reality. They assumed, like Hegel and Marx, that history is an integral component of any of these. Institutions, and humans, move and change in fundamental ways. The members of the institute were also committed to the idea that to understand contemporary society, you need both empirical research and theory. They opposed those who would just engage in theory without research (they introduced American-style empirical research to Germany when they returned after their exile at Columbia University during the war). But they also opposed positivism, the idea that all you have to do is follow the empirical world, and that's all that knowledge is.
Original members (* - indicates key member for our purposes):
Later figures:
And there are other figures who have sometimes been associated with the movement: