Charles de Secondat, the baron de Montesquieu, came from the French nobility. He received a Classical education and then studied law. In his first work, the Persian Letters, published in 1721, he used the format of two Persians supposedly traveling in western Europe and sending their impressions back home to enable him to criticise French institutions, especially the Catholic Church and the French monarchy. Much of the program of the French Enlightenment is contained in this work: the attack on traditional religion, the advocacy of religious toleration, the denunciation of slavery, and the use of reason to liberate human beings from their prejudices.
Voltaire was well received in English literary and social circles and was impressed by England. His Philosophic Letters on the English, written in 1733, expressed a deep admiration of English life, especially its freedom of the press, its political freedom, and its religious toleration. Although he clearly exaggerated the freedoms England possessed, in a roundabout way, Voltaire had managed to criticise many of the ills pressing France, especially royal absolutism and the lack of religious toleration and freedom of thought.
In his Treatise on Human Nature, David Hume argued that observation and reflection, grounded in "systematised common sense," made conceivable a "science of man." Careful examination of the experiences that constituted human life would lead to the knowledge of human nature that would make this science possible.
Montesquieu's most famous work, The Spirit of the Laws, was published in 1748. This treatise was a comparative study of governments in which Montesquieu attempted to apply the scientific method to the social and political arena to ascertain the "natural laws" governing the social relationships of human beings. Montesquieu distinguished three basic kinds of governments: republics, monarchy, and despotism. Montesquieu's praise and analysis of England's constitution that led to his idea of the importance of checks and balances created by means of a separation of powers. In large part, Montesquieu misread the English situation and insisted on a separation of powers because he wanted the nobility of France to play an active role in running the French government.
Denis Diderot's most famous contribution to the Enlightenment was the twenty-eight-volume Encyclopedia that he edited and called the "great work of his life." its purpose, according to Diderot, was to "change the general way of thinking." It became a major weapon of the philosophes' crusade against the old French society. In later editions, the price of the Encyclopedia was drastically reduced, dramatically increasing its sales and making it available to doctors, clergy, teachers, lawyers, and even military officers. The ideas of the Enlightenment were spread even further as a result.
The philosophe-historians broadened the scope of history from the humanists' preoccupation with politic. Politics still predominated in the work of Enlightenment historians, but they also paid attention to economic, social, intellectual, and cultural developments. As Voltaire explained in his masterpiece, The Age of Louis XIV: "It is not merely the life of Louis XIV that we propose to write; we have a wider aim in view. We shall endeavor to depict for posterity, not the actions of a single man, but the spirit of men in the most enlightened age the world has ever seen." In seeking to describe the "totality of past human experience," Voltaire initiated the modern ideal of social history.
Another influential treatise by Rousseau also appeared in 1762. Titled Emile, it is one of the Enlightenment's most important works on education. Written in the form of a novel, the work is really a general treatise "on the education of the natural man." Rousseau's fundamental concern was that education should foster rather than restrict children's natural instincts. Life's experiences had shown Rousseau the importance of the promptings of the heart, and what he sought was a balance between heart and mind, between sentiment and reason. This emphasis on heart and sentiment made him a precursor of the intellectual movement called Romanticism that dominated Europe at the beginning of the nineteenth century.
In his celebrated treatise The Social Contract, published in 1762, Jacques Rousseau tried to harmonise individual liberty with governmental authority. The social contract was basically an agreement on the part of an entire society to be governed by its general will. If any individual wished to follow his own self-interest, he should be compelled to abide by the general will. The general will represented a community's highest aspirations, whatever was best for the entire community. Thus, liberty was achieved through being forced to follow what was best for all people because, he believed, what was best for all was best for each individual.
Voltaire lent his prestige and skills as a polemicist to fighting cases of intolerance in France. The Calas affair was the most famous incident. Jean Calas was a Protestant from Toulouse who was accused of murdering his own son to stop him from becoming a Catholic. Tortured to confess his guilt, Calas died shortly thereafter. An angry and indignant Voltaire published devastating broadsides that aroused public opinion and forced a retrial in which Calas was exonerated when it was proved that his son had actually committed suicide. The family was paid an indemnity, and Voltaire's appeals for toleration appeared all the more reasonable. In 1763, Voltaire penned his Treatise on Toleration, in which he argued that religious toleration had created no problems for England and Holland and reminded governments that "all men are brothers under God."
Appalled by the unjust laws and brutal punishments of their times, some philosophes sought to create a new approach to justice. The most notable effort was made by an Italian philosophe, Cesare Beccaria. In his essay On Crimes and Punishments, written in 1764, Beccaria argued that punishments should serve only as deterrents, not as exercises in brutality. Beccaria was also opposed to the use of capital punishment. It was spectacular, but it failed to stop others from committing crimes.
Baron Paul d'Holbach was a wealthy German aristocrat who settled in Paris, and preached a doctrine of strict atheism and materialism. In his System of Nature, written in 1770, he argued that everything in the universe consisted of matter in motion. Human beings were simply machines; God was a product of the human mind and was unnecessary for leading a moral life. People needed only reason to live in this world. Holbach shocked almost all of his fellow philosophes with his uncompromising atheism. Most intellectuals remained more comfortable with deism and feared the effect of atheism on society.
The best statement of laissez-faire was made in 1776 by a Scottish philosopher, Adam Smith, in his Wealth of Nations. In the process of enunciating three basic principles of economics, Smith presented a strong attack on mercantilism. He condemned the mercantilist use of tariffs to protect home countries. If one country can supply another country with a product cheaper than the latter can make it, it is better to purchase than to produce it. To Smith, free trade was a fundamental economic principle. Smith's second principle was his labour theory of value. He claimed that gold and silver were not the source of a nation's true wealth, but unlike the Physiocrats, he did not believe that soil was either. Labour constituted the true wealth of a nation, he believed. Smith believed that the state should not interfere in economic matters. He believed the government had three basic functions: to protect society from invasion, defend individuals from injustice and oppression, and keep up certain public works that private individuals could not afford.
Philosophe-historians sought to instruct as well as entertain. Their goal was to help civilise their age, and history could play a role by revealing its lessons according to their vision. Their emphasis on science and reason and their dislike of Christianity made them less than sympathetic to the period we call the Middle Ages. This is particularly noticeable in the six-volume Decline and Fall of the Roman Empire by Edward Gibbon. Although Gibbon thought that the decline of Rome had many causes, he portrayed the growth of Christianity as a major reason for Rome's eventual collapse. Gibbon believed in the idea of progress and, in reflecting on the decline and fall of Rome, expressed his optimism about the future of European civilisation and the ability of Europeans to avoid the fate of the Romans.
The strongest statement for the rights of women in the eighteenth century was advanced by the English writer Mary Wollstonecraft, viewed by many as the founder of modern European feminism. In Vindication of the Rights of Woman, written in 1792, Wollstonecraft pointed out two contradictions in the views of women held by such Enlightenment thinkers as Rousseau. To argue that women must obey men, she said, was contrary to the beliefs of the same individuals that a system based on the arbitrary power of monarchs over their subjects or slave owners over their slaves was wrong. The subjection of women to men was equally wrong. In addition, she argued, the Enlightenment was based on the ideal that reason is innate in all human beings. If women have reason, then they are entitled to the same rights that men have. Women, Wollstonecraft declared, should have equal rights with men in education and in economic and political life as well.
Marie-Jean de Condorcent, another French philosophe, made an exaggerated claim for progress. Condorcet was a victim of the turmoil of the French Revolution and wrote his chief work, The Progress of the Human Mind, while in hiding during the Reign of Terror. His survey of human history convinced him that humans had progressed through nine states of history. Now, with the spread of science and reason, humans were about to enter the tenth state, one of perfection, in which the will see that "there is no limit to the perfecting of the powers of man; that human perfectibility is in reality indefinite, that the progress of this perfectibility...has no other limit than the duration of the globe upon which nature has placed us."