SummaryIn a nutshell, the present essay claims this: First, the classical problem of knowledge has recently shifted from, How do I know? to, How do we know?–from psychology to sociology. As a phenomenological matter this is a great improvement, as a solution to the problem of rationality it is erroneous and immoral. The problem, (Why) should I act, believe, etc., this or that? is answered: You should do so on the authority of your reason. But change the problem of rationality in accord with the change in the problem of knowledge, and ask, (Why) should we–rather than I–act or believe as we do? and the answer is clear: We should act and believe as we do, because our society is as it is, and should be as it is. This is clearly the same as, we should because we should. Not very enlightening.Sociologism appears as the authoritarian solution to the problem of rationality in works of Polanyi and Kuhn; a variant of it appears as a liberal theory in the studies of Popper and his former students who, however, do not offer any positive theory of what to believe or do; rather, they offer a negative theory of what to reject. They view this as a better solution to the problem of rationality, if not even a better formulation of it (not what and why should I/we etc., but what and why should I/we not etc.).