Statistics on murder rates showed that modern self-restraint had replaced a medieval tendency toward carnage, while social expectations had accentuated the positive in human nature, keeping “inner demons” in check. No one could deny that the arguments were well-packaged and well-written. Violence, he aimed to show, had long been in decline and had now reached an all-time low. In his 2011 book, The Better Angels of Our Nature, he proposed that by one crucial measure, human life was improving across the world.

The Harvard psychologist Steven Pinker has long been a loud votary of progress. The lesson from this history is not necessarily that progress is unavailable, but that to believe in it is not easy. Yet things went south in the rise of empire and the victory of reaction, the explosion of a dehumanizing brand of capitalism, and two world wars, capped by Auschwitz and Hiroshima. After the Scientific Revolution, priestcraft and superstition lost credibility, and after American independence, the French Revolution established hopes that liberty and equality for all were on the way, putting an end to material penury and social hierarchy. Philosophers of the Enlightenment imagined that it was possible to break the chains of oppression and bring about the emancipation of all people. Belief in human progress has always depended on a kind of provisional faith.

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