Book IV of Adam Smith's Wealth of Nations concerns two rival economic theories, Mercantilism and Physiocracy. The latter, François Quesnay's system, occupies only the ninth and final chapter, and it begins with a stunning dismissal. Yet, fifteen pages later, Smith praises this theory to the skies. That cries out for explanation. Like Mercantilism, Smith's system emphasizes commerce, whereas Quesnay's is confined to agriculture. But like Physiocracy, Smith's system is built on individual liberty, whereas Mercantilism is one of government control. Despite (...) his initial put-down, Smith is naturally inclined more toward Quesnay's philosophy. And the main thesis of my paper is to suggest one reason for this that has not previously been brought to light, and that can explain Smith's extravagant praise for it. Quesnay employs a Newtonian scientific method different from the one emphasized in Smith's early ‘Astronomy’ treatise, a method Smith first prominently introduced a decade after his meetings with Quesnay, in Wealth of Nations and Smith's eulogy for Hume, and in the sixth edition of his Theory of Moral Sentiments. (shrink)