In 1784, in an essay titled “What Is Enlightenment?,” the German philosopher Immanuel Kant gave widespread currency to a term that had been in the making for several decades. The term enlightened century had become common in the 1760s. The Enlightenment thus gave itself its own name, and the name clearly had propaganda value. The philosophes associated Enlightenment with philosophy, reason, and humanity; religious tolerance; natural rights; and criticism of outmoded customs and prejudices. They tied Enlightenment to “progress” and to the “modern,” and it came into question, just as these other terms did, when events cast doubt on the benefits of progress and the virtues of modernity. Although some opposed the Enlightenment from the very beginning as antireligious, undermining of authority, and even atheistic and immoral, the French Revolution of 1789 galvanized the critics of Enlightenment who blamed every excess of revolution on Enlightenment principles.

For most of the nineteenth and twentieth centuries, condemnation of the Enlightenment came from right-wing sources. Some of the more extreme of these critics denounced a supposed “Jewish-Masonic conspiracy,” believing that Jews and Freemasons benefited most from the spread of Enlightenment principles and worked in secret to jointly undermine Christianity and established monarchical authorities. Adolf Hitler and his followers shared these suspicions, and during World War II the Germans confiscated the records of Masonic lodges in every country they occupied. They sent the documents back to Berlin so that a special office could trace the links of this supposed conspiracy. They found nothing.

After the catastrophes of World War II, the Enlightenment came under attack from left-wing critics. They denounced the Enlightenment as “self-destructive” and even “totalitarian” because its belief in reason led not to freedom but to greater bureaucratic control. They asked why mankind was sinking into “a new kind of barbarism,” and they answered, “Because we have trusted too much in the Enlightenment and its belief in reason and science.” The Nazis used bureaucratic control and technology to kill millions of Jews and others they deemed inferior. Science gave us the atomic bomb and factories that pollute the atmosphere. These criticisms of the Enlightenment show how central the Enlightenment remains to the very definition of modern history.