All sciences are based on principles that are essentially unprovable, and that can only be validated by practical use, where they are the basis of extensive research that can either succeed or fail. This is a problem that Montaigne had already identified when he said that it is a form of torture, and it means that any assessment of a principle’s validity, and the lack of or limits to its validity, cannot usually be made in the short term. This is why science can allow false ideas to emerge and even to continue for some time. But we must distinguish this false knowledge from the sort – such as astrology – that derives from what are well-known to be weak principles, but which continue to persist in the public domain because they are supported by public demand and by the entrepreneurs who exploit it. Because the false knowledge derived from the difficulties involved in validating principles benefits, in the short or longer term, from the authority of science and scientists it can and sometimes does have an insidious and significantly greater effect on social life than the false knowledge of the accepted pseudo-sciences. We provide brief monographs here about some of the principles adopted by the humanities and social sciences that are the subject of this article. There is no problem in understanding why these principles have been endorsed. But in their more questionable forms they have led to bad habits that have had grave political and social effects. The difficulties which validation principles encounter do not justify in any way, however, the thriving contemporary skepticism about science nurtured by postmodernism, in relation to the human and social sciences as much as the natural sciences.