The philosophy of social science emerged after the philosophy of science, and to some extent is defined by its preoccupations. The philosophy of science is concerned about the nature of the objects under investigation (their reality and character) and the nature of reliable scientific knowledge (what counts as true knowledge? what methods will lead us to it?). Since the philosophy of science has a long history as the "standard" of scientific knowledge, the social sciences have always existed as a poor second cousin. The object they were investigating just wasn't as clear or determinate, and the nature of reliable knowledge was just not as clear also. So, the social sciences have always either aspired to true scientific knowledge by making their object clear and their methods reliable, or they have redefined themselves so that they do not have to match the objects and methods of natural science.
Cultural studies and critical theory are suspicious of this whole process. Starting with natural science as the standard of knowledge is unacceptable.
There are several central questions in the philosophy of social science that cultural studies takes a stand on:
No. The world of human action and meaning does not yield the same kind of knowledge as the natural world. It is important to realize, though, that we can treat the human world like the natural world, looking for mechanistic causal connections and explanations. We can often find them as well. But we have to reduce the human world to something less than human to do it.
No. Whereas science likes to imagine itself as the dispassionate pursuit of knowledge for its own sake, cultural studies holds that such science has refused to recogize that it is embedded in a cultural world. So, it is not that a person can study the natural world dispassionately, but the cultural world requires normative statements. In fact, cultural studies holds that all human activity is meaningful and normative. So, you can do a cultural studies of physics, for instance.
No. There is no objectivity in the classical sense, in which our observations of a phenomenon are completely separate from that phenomenon. Inquiring about culture requires that we think about the questions we ask about culture, the assumptions we make. We are embedded in that culture. Ultimately to ask about any human meaning is to ask about all human meaning, including our own.
No. To explain means to limit freedom. Mechanisms are not free - thinking in terms of causation means to recognize that things act the way they act because something else made it happen. Most attempts to explain human action and meaning amount to reducing human freedom. It is worth noting that critical theory, to some extent, also imagines humans as limited in freedom, in that humans are seen as part of a system of meaning that they did not create. However, humans are not simply unknowing participants in that system. They choose to act within the rules of a game. Actor-centered sociology also holds this model, but it differs from critical theory in that critical theory has a more political and radical agenda.