On quite liberal grounds, one would expect the concept knows to have a non-trivial analysis in somehow more basic terms. Not all concepts have such analyses, on pain of infinite regress; the history of analytic philosophy suggests that those of most philosophical interest do not. ‘Bachelor’ is a peculiarity, not a prototype. Attempts to analyze the concepts means and causes, for example, have been no more successful than attempts to analyze the concepts knows, succumbing to the same pattern of counterexample and epicycles. The analyzing concept does not merely fail to be the same as the concept to be analyzed; it fails even to provide a necessary and sufficient condition for the latter. The pursuit of analyses is a degenerating research programme.

Timothy Williamson, Knowledge and Its Limits