But these additions are of small importance compared with the introduction of the theory of stock or capital and unproductive labour in Book II , the slipping of a theory of distribution into the theory of prices towards the end of Book I , chapter vi , and the emphasising of the conception of annual produce. These changes do not make so much real difference to Smith’s own work as might be supposed; the theory of distribution, though it appears in the title of Book I , is no essential part of the work and could easily be excised by deleting a few paragraphs in Book I , chapter vi , and a few lines elsewhere; if Book II were altogether omitted the other Books could stand perfectly well by themselves. But to subsequent economics they were of fundamental importance. They settled the form of economic treatises for a century at least.
They were of course due to the acquaintance with the French Économistes which Adam Smith made during his visit to France with the Duke of Buccleugh in 1764–6. It has been said that he might have been acquainted with many works of this school before the notes of his lectures were taken, and so he might. But the notes of his lectures are good evidence to show that as a matter of fact he was not, or at any rate that he had not assimilated their main economic theories. When we find that there is no trace of these theories in the Lectures and a great deal in the Wealth of Nations , and that in the meantime Adam Smith had been to France and mixed with all the prominent members of the “sect,” including their master, Quesnay, it is difficult to understand why we should be asked, without any evidence, to refrain from believing that he came under physiocratic influence after and not before or during his Glasgow period.