When I sat in on a seminar on causation by David Lewis, he made a point which has stuck with me. He commented that it was a peculiarity of philosophers to think that what could not be done by a clever person in a half hour of work could not be done at all. He mentioned the specific example of giving a conceptual analysis of the concept of a chair, borrowing the example of course from Wittgenstein (and it was brought to mind because I'm re-reading my Kuhn, and Kuhn mentions this bit of Wittgenstein lore). Wittgenstein, and Kuhn, and many others, have believed that it is impossible to provide an adequate conceptual analysis of "chair," to provide a set of necessary and sufficient conditions for being a chair which would adequately cover the range of cases.
To this claim of impossibility, Lewis expressed skepticism. Suppose someone were to establish a multi-million dollar foundation devoted to the conceptual analysis of "chair," and pay the vast salaries needed to draw top logicians, linguists, metaphysicians, and experienced makers of furniture together to investigate the problem over the course of years. Is it really reasonable to declare in advance, based on our armchair Wittgensteinian speculations, that they would definitely not produce anything adequate in the end?
Of course, nobody would ever do that, and certainly if Wittgenstein's point was only that we need not have a conceptual analysis in hand to be able to make adequate use of a concept, then there is no cause to quibble (except with any notion that this was a strikingly novel thought). But I share Lewis' skepticism about the stronger claim, that the conceptual analysis simply couldn't be done. Further, as Socrates told Meno, we will be better and braver if we believe that it is possible to know and inquire, than if we believe the arguments of the skeptics that it is impossible to know and so embrace idleness.