One of the great literary landmarks of the Enlightenment was Baron D'Holbach's book, The System of Nature, which was published in 1770. There are many remarkable things in it, but none more so than its first sentence: "The source of man's misery is his ignorance of nature". On the contrary, it was nothing less than the central claim of the Enlightenment, somewhat unguardedly expressed. The Encyclopedists and their allies never dreamed of advocating Enlightenment for its own sake. They assumed that Enlightenment needed justification, and the justification of it always was that it improves human life. The Enlightenment had, then, an ethical justification of itself, as well as a utilitarian one. Accordingly, the utilitarian justification of Enlightenment had to be more and more exclusively insisted upon. It was in this way that the Enlightenment became committed to, or rather became identified with, a certain promise: the promise that, by increasing knowledge, happiness would be increased.