The political implications of the Enlightenment were surprisingly muted at the time. Almost every society in Europe exercised official censorship, and many philosophes had to publish their more provocative works using pseudonyms, sometimes resorting to illegal publishing operations and book smugglers in order to evade that censorship (not to mention their own potential arrest). Philosophes tended to openly attack the most egregious injustices they perceived in royal governments and the organized churches, but at the same time their skepticism about the intellectual abilities of the common people was such that almost none of them advocated a political system besides a better, more rational version of monarchy. Likewise, philosophes were quick to salute (to the point of being sycophantic at times) monarchs who they thought were living up to their hopes for the ideal of rational monarchy.
In turn, various monarchs and nobles were attracted to Enlightenment thought. They came to believe in many cases in the essential justice of the arguments of the philosophes and did not see anything contradictory between the exercise of their power and enlightenment ideas. That said, monarchs tended to see “enlightened reforms” in terms of making their governments more efficient. They certainly did not renounce any of their actual power, although some did at least ease the burdens on the serfs who toiled on royal lands.
One major impact that Enlightenment thought unquestionably had on European (and, we should note, early American) politics was in the realm of justice. A noble from Milan, Cesare Bonesana, wrote a brief work entitled On Crimes and Punishment in 1764 arguing that the state’s essential duty was the protection of the life and dignity of its citizens, which to him included those accused of crimes. Among other things, he argued that rich and poor should be held accountable before the same laws, that the aim of the justice system should be as much to prevent future crimes as to punish past ones, and that torture was both barbarous and counter-productive. Several monarchs in the latter part of the eighteenth century did, in fact, ban torture in their realms, and "rationalized" justice systems slowly evolved in many kingdoms during the period.
Perhaps the most notable “enlightened monarch” was Frederick II (the Great) of Prussia (r. 1740 – 1786). A great lover of French literature and philosophy, he insisted only on speaking French whenever possible (he once said that German was a language only useful for talking to one's horse), and he redecorated the Prussian royal palace in the French style, in which he avidly hosted Enlightenment salons. Frederick so impressed the French philosophes that Voltaire came to live at his palace for two years until the two of them had a falling out. Inspired by Enlightenment ideas, he freed the serfs on royal lands and banned the more onerous feudal duties owed by serfs owned by his nobles. He also rationalized the royal bureaucracy, making all applicants pass a formal exam, which provided a limited path of social mobility for non-nobles.
Another ruler inspired by Enlightenment ideas was the Tsarina Catherine the Great (r. 1762 - 1796) of Russia. Catherine was a correspondent of French philosophes and actively cultivated Enlightenment-inspired art and learning in Russia. Hoping to increase the efficiency of the Russian state, she expanded the bureaucracy, reorganized the Russian Empire’s administrative divisions, and introduced a more rigorous and broad education for future officers of the military. She also created the first educational institution for girls in Russia, the Smolny Institute, admitting the daughters of nobles and, eventually, well-off commoners. Her enthusiasm for the Enlightenment dampened considerably as the French Revolution began in 1789, however, and while Russian nobles found their own privileges expanded, the vast majority of Russian subjects remained serfs. Like Frederick of Prussia, Catherine’s appreciation for “reason” had nothing to do with democratic impulses.
One major political theme to emerge from the Enlightenment that did not require the goodwill of monarchs was the idea of human rights (or “the rights of man” as they were generally known at the time). Emerging from a combination of rationalistic philosophy and what historians describe as new “sensibilities” - above all the recognition of the shared humanity of different categories of people - concepts of human rights spread rapidly in the second half of the eighteenth century. In turn, they fueled both demands for political reform and helped to inspire the vigorous abolitionist (anti-slavery) movement that flourished in Britain in particular. Just as torture came to be seen by almost all Enlightenment thinkers as not just cruel, but archaic and irrational, so slavery went from an unquestionable economic necessity to a loathsome form of ongoing injustice. Just as the idea of human rights would soon inspire both the American and French Revolutions in the closing decades of the eighteenth century, the antislavery movements of the time would see many of their objectives achieved in the first few decades of the nineteenth (Britain would ban the slave trade in 1807 and slavery itself in 1833, although it would take the American Civil War in the 1860s to end slavery in the United States).