The 18th century in France saw the emergence of economics as a science and the first school of economic thought: Physiocracy. Adam Smith trained in economics during this period, and French economists were recognized globally as leaders. However, this century is remembered more as the century of philosophy than of economics. While the Physiocratic movement aligned, in its ambitions, with Enlightenment philosophy, the attitudes of the philosophes—especially Diderot and Voltaire—deserve close examination. We will see that the Enlightenment thinkers significantly contributed to spreading the idea of laissez-faire in France.

The most famous achievement of Enlightenment philosophy is without a doubt the Encyclopédie by Diderot and d'Alembert.

Naturally, the economic articles were written by economists. For the early volumes, Diderot turned to Forbonnais, then enlisted liberal economists: first François Quesnay (who contributed articles like "Grains", "Fermiers", "Hommes"—the last one unpublished), then Turgot (who wrote "Foires et marchés"). These writings are of great importance. In his articles, Quesnay laid the groundwork for what would become Physiocratic doctrine. Along with his Tableau économique, these remain his most famous works. Turgot, still young at the time, developed the idea of laissez-faire in his article, criticizing state intervention in market organization.

In many other articles of the Encyclopédie, philosophes, especially Diderot, defend the ideal of liberty in all areas: religion, politics, and economics.

Freedom of labor, especially in opposition to the guild system, was a recurring theme in various entries such as Arts, Métier, and Communauté.

Diderot's path in economic theory is a curious one. In the Encyclopédie, he was a staunch advocate for economic freedom and was the one who sought the collaboration of liberal economists, as confirmed by a letter outlining the articles Turgot might write for him. In the early years of Physiocracy, he was both a supporter and a promoter of Quesnay's school. In 1769 and 1770, he wrote for Les Ephémérides du Citoyen, to the great dismay of his anti-liberal philosopher friends, like Melchior Grimm; however, he soon distanced himself from the group. Enthralled by the vibrant intellect of Abbot Galiani, he helped him publish his book on the grain trade in French, just as Galiani was about to return to Italy.

This book would become the fiercest attack ever made against Physiocratic ideas, delivering a major blow to the movement. Later, Diderot defended Galiani against Abbot Morellet, a close ally of the Physiocrats, in his Apology of Galiani. A few years later, during Turgot's ministry, Diderot was seen applauding the establishment of freedom of labor through the abolition of guilds. At this point, Diderot, an artisan's son, found himself in agreement with the liberal economists and wrote a scathing letter to Galiani, who claimed that freedom of labor would ruin French industry within twenty or thirty years. In light of the Industrial Revolution, history suggests otherwise. Having returned to the liberal economists' side, Diderot no longer enjoyed their trust and remained isolated. A very telling moment is a letter he sent to Dupont de Nemours in 1774, where he writes:

Voltaire followed a similar path, marked by a lack of consistency in his economic views. He admired Vincent de Gournay, corresponded with economists (including Dupont de Nemours and Turgot), and appreciated the Physiocrats-especially for their praise of agriculture. He extolled them in a Diatribe to the Author of the Ephémérides. However, he later criticized their idea of a single land tax in his satirical work The Man of Forty Crowns, which also stirred significant controversy. Finally, like Diderot, he celebrated Turgot's ministry, calling it a golden age and praising his two great decrees on freedom of labor and free trade.

In the end, the philosophes' relationship with economic thought is mixed. Despite their praises and critiques of liberal economic ideas, they played a role in bringing these ideas into the broader intellectual discourse of the Enlightenment. In this way, whether intentionally or not, they helped advance the notion of laissez-faire right up to the Revolution.