Suppose we took the view that the social sciences ought to provide sufficient conceptual and methodological tools to analyze and explain any kind of social behavior. This would be a certain kind of completeness: not theoretical or explanatory completeness, in the sense of having a finished set of theories that can explain everything, but conceptual completeness, in the sense that there are sufficient conceptual resources to give a basis for describing every form of social behavior, and methodological completeness, in the sense that for every possible research question there are starting point for inquiry in the social sciences. And, finally, suppose we stipulate that there are always new hypotheses to be discovered and new theories to be invented.
If this is one of the ultimate aspirations for the social sciences, then we can ask -- how close is the current corpus of social science research and knowledge to this goal?
One possible answer is that we have already reached this goal. The conceptual resources of anthropology, economics, political science, and sociology serve as a "fish-scale" system of conceptual coverage that gives us a vocabulary for describing any possible configuration of social behavior. And the most basic ideas about empirical research, causal reasoning, hypothetical thinking, and interpretation of meaning give us a preliminary basis for probing and investigating any of the "new" phenomena we might discover.
Another possible answer goes in the opposite direction. The concepts of the social science disciplines are parochial and example-based. When new forms of social interaction emerge we will need new concepts on the basis of which to describe and represent these social behaviors. So concepts and empirical knowledge must go hand in hand, and new discoveries will stimulate new concepts as well.
Consider this thought experiment. Suppose the social sciences had developed to this point minus micro-economics. The reduced scheme would involve many aspects of behavior and thought, but it would have omitted the category of "rational self-interest." Is this a possible scenario? Would the reduced set be complete in the sense described above? And what kind of discovery would be required in order for these alternative-world social scientists to progress?
The incompleteness of alternative-world social science is fairly evident. There would be important ranges of behavior that would be inscrutable without the concept of rational self-interest (market equilibria, free-rider problems). And the solution would appear fairly evident as well. These gaps in explanatory scope would lead investigators to ask, what is the hidden factor we are not considering? And they would be led to discover the concept of rational self-interest.
The moral seems to be this: it is always possible that new discoveries of anomalous phenomena will demonstrate the insufficiency of the current conceptual scheme. And therefore there is never a point at which we can declare that science is now complete, and no new concepts will be needed.
At the same time, we do in fact have a rough-and-ready pragmatic confidence that the social sciences as an extended body of theories, concepts, and results have pretty well covered the primary scope of human behavior. And this suggests a vision of the way the social sciences cover the domain of the social as well: not as a comprehensive deductive theory but rather as an irregular, overlapping collection of concepts, methods, and theories -- a set of fish-scales rather than an architect's blueprint for all social phenomena.