Jefferson confirmed his enlightenment in his 28 October 1785 letter to James Madison. In it Jefferson announced his coming out by deploying a set of enlightened ideas he learned from Cabanis. “Whenever there are in any country uncultivated lands and unemployed poor,” Jefferson announced, “it is clear that the laws of property have been so far extended as to violate the natural right. The earth is given as a common stock for man to labor and live on.” This was not a new subject for Jefferson—he touched on it in his 1774 analysis of the “Rights of British America.” In his letter to Madison, however, Jefferson frames the issue in specifically enlightened terms.
John Locke had begun his argument for majoritarian government, which he presented in his Second Treatise of Government, with the “common stock” idea. “I shall endeavor to show,” he stated in paragraph 25, “how men might come to have a property in several parts of that which God gave mankind in common.” Rousseau excerpted Locke’s idea into his second great work, On the Origin of Inequity Among Men, which he wrote in 1755. With this paper, Rousseau joined the enlightened assault on the antiquated, economically stifling, system of land tenure. Herbert Sloan gave a history of this attack in the second chapter of Principle & Interest, where he described the business as prying off “the dead hand of the past.” Rousseau configured the issue in terms of his own idiosyncratic perspective as a member of France’s renting class. For Rousseau the issue was the social inequality that attended unequal distribution of property. He began the second section of his essay with these words:
"The first man who, having enclosed a piece of ground, bethought himself of saying This is mine, and found people simple enough to believe him, was the real founder of civil society. From how many crimes, was the real founder of civil society. From how many crimes, wars and murders, form how many horrors and misfortunes might not any one have saved mankind, by pulling up the stakes, or filling up the ditch, and crying to his fellows, “Beware of listening to this impostor: you are undone if you once forget that the fruits of the earth belong to us all, and that the earth itself to nobody.” But there is great probability that things had then already come to such a pitch, that they could no longer continue as they were; for the idea of property depends on many prior ideas, which could only be acquired successively . . . "
Adam Smith concluded his three-part inquiry into the nature and causes of the wealth of nations with a section entitled Of the Different Progress of Opulence in Different Nations. This section has decidedly French themes. In addition to discussions of progress and the “wantonness of plenty”, Smith assays the economic relationship between towns and the country that surrounds them, the relationship between agriculture and commerce, and “how the towns improve the country.” In a discussion he calls The Discouragement of Agriculture, Smith addresses the problems of primogeniture and entailment. “They are founded upon the most absurd of suppositions,” he observed, “the supposition that every successive generation of men have not an equal right to the earth, and to all that it possesses; but that the property of the present generation should be restrained and regulated according to the fancy of those who died perhaps five hundred years ago.”
I consider it likely that Jefferson read this passage in the first edition of The Wealth of Nations, which he purchased while he was in France. Jefferson reformulated Smith’s condemnation of the antiquated system of land tenure in the famous letter he wrote to James Madison on 6 September 1789. He began his reinterpretation of Smith’s objection somewhat disingenuously by announcing that, “the question of whether one generation has a right to bind another, seems never to have been started either on this or our side of the water.” Having introduced the issue, he presented it in these words, “I set out on this ground which I suppose to be self evident, ‘that the earth belongs in usufruct to the living;’ that the dead have neither powers nor rights over it. The portion occupied by an individual ceases to be his when himself ceases to be, and reverts to the society.”
When Jefferson addressed the issue at the end of October 1785, he had just become enlightened. By the time he returned to it in September of 1789, he had become an active member of the reform movement that was unknowingly creating the organization that would soon overthrow France’s hierarchical system.