From losing our minds metaphysically it was but a short step to losing them ethically. The wisdom of the ages had said that those with sharper faculties should use them for higher purposes, and certainly not self-aggrandisement. Self-knowledge was important to offset the tendency to spend one’s time looking for the motes in other people’s eye, habitually projecting our problems elsewhere. This is best summarised in Hume’s famous dictum from his Treatise of Human Nature (§2.3.3): ‘Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them.’ There is no finer or more precise statement of our modern Enlightenment ethic; the modern mind spend its whole time dreaming up the most fabulous justifications for its sentiments and this habit has become so entrenched that we are no longer aware of it. The most powerful shared sentiment that moderns have is the idea that we are Enlightened, of course, far more sensitive, free thinking, wise and intelligent than anyone who has lived before or anyone today who doesn’t share our Enlightened values. It follows from this that our Enlightenment is guaranteed, that it will be a self-fulfilling prophesy.
Rousseau took this idea into the political sphere with his idea of the ‘noble savage’ (actually a term coined by Dryden), ‘born free but everywhere in chains’ (The Social Contract): all man needed was a perfect republic in order for his innate goodness to manifest. To make all of this fly he needed a Social Contract between the citizens and a Sovereign republic that would reflect the General Will of the people. The General Will would have to be omniscient to justify Sovereignty (it would henceforth have a monopoly on violence—a kind of omnipotence); that none of this quite hang together doesn’t seem to have bothered anybody too much, but it certainly formed the blueprint for the modern nation state.
Both Hume and Kant made it clear in their prefaces (to the Treatise and the Critique) that they saw the natural sciences as their model of perfection and sought to replicate their success in the humanities. It was predictable that a people who have, like no other, mastered physical causation (on an industrial scale), have built a civilisation based on Hume’s dictum, harnessing our intelligence, instrumentally, to shape the environment according to our sentiments.