We are entering, we are told, a post-liberal age. So-called illiberal democracy and authoritarian populism are in the political ascendant; the shelves of our bookshops groan with the work of attention-grabbing thinkers insisting that permissiveness, multiculturalism and "identity politics" have failed us and that we must now fall back on some notion of tradition. We have had our fun, and now it's time to get serious, to shore our fragments against...