The Enlightenment was a movement of international dimensions, with thinkers traversing borders in a constant exchange of visits, letters, and printed materials. Voltaire alone wrote almost eighteen thousand letters to correspondents across Europe. The Republic of Letters, as this international group of scholars and writers was called, was a truly cosmopolitan set of networks stretching from western Europe to its colonies in the Americas, to Russia and eastern Europe, and along the routes of trade and empire to Africa and Asia.

Within this broad international conversation, scholars have identified regional and national particularities. Outside of France, many strains of Enlightenment thought — Protestant, Catholic, and Jewish — sought to reconcile reason with faith, rather than emphasizing the errors of religious fanaticism and intolerance. Some scholars point to a distinctive “Catholic Enlightenment” that aimed to renew and reform the church from within, looking to divine grace rather than human will as the source of social progress.

The Scottish Enlightenment, centered in Edinburgh, was marked by an emphasis on common sense and scientific reasoning. After the Act of Union with England in 1707, Scotland was freed from political crisis to experience a vigorous period of intellectual growth. Scottish intellectual revival was also stimulated by the creation of the first public educational system in Europe.

A central figure in Edinburgh was David Hume (1711–1776), whose civic morality and religious skepticism had a powerful impact at home and abroad. Hume strove to apply Newton’s experimental methods to what he called the “science of man.” Building on Locke’s writings on learning, Hume argued that the human mind is really nothing but a bundle of impressions. These impressions originate only in sensory experiences and our habits of joining these experiences together. Since our ideas ultimately reflect only our sensory experiences, our reason cannot tell us anything about questions that cannot be verified by sensory experience (in the form of controlled experiments or mathematics), such as the origin of the universe or the existence of God. Hume further argued, in opposition to Descartes, that reason alone could not supply moral principles but that they derived instead from emotions and desires, such as feelings of approval or shame. Hume’s rationalistic inquiry thus ended up undermining the Enlightenment’s faith in the power of reason by emphasizing the superiority of the passions over reason in driving human behavior.

Hume’s emphasis on human experience, rather than abstract principle, had a formative influence on another major figure of the Scottish Enlightenment, Adam Smith (1723–1790). In his Theory of Moral Sentiments (1759), Smith argued that social interaction produced feelings of mutual sympathy that led people to behave in ethical ways, despite inherent tendencies toward self-interest. By observing others and witnessing their feelings, individuals imaginatively experienced such feelings and learned to act in ways that would elicit positive sentiments and avoid negative ones. Smith believed that the thriving commercial life of the eighteenth century was likely to produce civic virtue through the values of competition, fair play, and individual autonomy. In An Inquiry into the Nature and Causes of the Wealth of Nations (1776), Smith attacked the laws and regulations created by mercantilist governments that, he argued, prevented commerce from reaching its full capacity (see Chapter 18). For Smith, ordinary people were capable of forming correct judgments based on their own experience and should therefore not be hampered by government regulations. Smith’s economic liberalism became the dominant form of economic thought in the early nineteenth century.

Inspired by philosophers of moral sentiments, like Hume and Smith, as well as by physiological studies of the role of the nervous system in human perception, the celebration of sensibility became an important element of eighteenth-century culture. Sensibility referred to an acute sensitivity of the nerves and brains to outside stimulus that produced strong emotional and physical reactions. Novels, plays, and other literary genres depicted moral and aesthetic sensibility as a particular characteristic of women and the upper classes. The proper relationship between reason and the emotions (or between Sense and Sensibility, as Jane Austen put it in the title of her 1811 novel) became a key question.

After 1760 Enlightenment ideas were hotly debated in the German-speaking states, often in dialogue with Christian theology. Immanuel Kant (1724–1804), a professor in East Prussia, was the greatest German philosopher of his day. Kant posed the question of the age when he published a pamphlet in 1784 titled What Is Enlightenment? He answered, “Sapere Aude (dare to know)! ‘Have the courage to use your own understanding’ is therefore the motto of enlightenment.” He argued that if intellectuals were granted the freedom to exercise their reason publicly in print, enlightenment would surely follow. Kant was no revolutionary; he also insisted that in their private lives, individuals must obey all laws, no matter how unreasonable, and should be punished for “impertinent” criticism. Like other Enlightenment figures in central and east-central Europe, Kant thus tried to reconcile absolutism and religious faith with a critical public sphere.

Northern Europeans often regarded the Italian states as culturally backward, yet important developments in Enlightenment thought also took place in the Italian peninsula. After achieving independence from Habsburg rule (1734), the kingdom of Naples entered a period of intellectual flourishing as reformers struggled to lift the heavy weight of church and noble power. In northern Italy a central figure was Cesare Beccaria (1738–1794), a nobleman educated at Jesuit schools and the University of Pavia. His On Crimes and Punishments (1764) was a passionate plea for reform of the penal system that decried the use of torture, arbitrary imprisonment, and capital punishment and advocated the prevention of crime over its punishment. The text was quickly translated into French and English and made an impact throughout Europe.