The attacks of September 11 oblige us to revise a prevalent view of religion as harmless and incompatible with rational forms of knowledge. Three modes of knowledge coexist today: theological knowledge involves adhesion to a system of beliefs; technological and natural science knowledge is value-free and neutral with regard to beliefs; lastly, knowledge in philosophy, social and human sciences relates to values, transcends national and cultural specificities and involves freedom and reason. Is this latter form of knowledge more apt to preserve one's critical conscience than other modes of knowledge? History does not, alas, corroborate this theory. All three knowledge modes, taken separately, lack both a wider rationality which would enable them to legitimize their actions in light of universal criteria, and the properties of democratic debate, the only way to avoid pathologies in thought, be they of a religious or scientific nature. In a post-secular society, religions resist all forms of secularizing influences. A true secular society is, however, able to preserve the contents of religion without destroying them.