The greatest work dealing with social problems, that Britain produced in the eighteenth century, was Adam Smith's Wealth of Nations, and his luminous exposition of the effects of the division of labour was the most considerable contribution made by British thinkers of the age to the study of human development. It is much more than a treatise on economic principles; it contains a history of the gradual economic progress of human society, and it suggests the expectation of an indefinite augmentation of wealth and well-being. Smith was entirely at one with the French Economists on the value of opulence for the civilisation and happiness of mankind. But it was indirectly perhaps that his work contributed most effectively to the doctrine of the Progress of collective mankind. [Footnote: It has been observed by Mr. Leslie Stephen that the doctrine of the rights of man lies in the background of Adam Smith's speculations.] His teaching that the free commercial intercourse of all the peoples of the world, unfettered by government policies, was to the greatest advantage of each, presented an ideal of the economic "solidarity" of the race, which was one element in the ideal of Progress. And this principle soon began to affect practice. Pitt assimilated it when he was a young man, and it is one of the distinctions of his statesmanship that he endeavoured to apply the doctrines of his master so far as the prevailing prejudices would allow him. 3. A few writers of less weight and fame than Hume or Smith expressly studied history in the light of Progress. It would not help us, in following the growth of the idea, to analyse the works of Ferguson, Dunbar, or Priestley. [Footnote: In his Essay on the History of Civil Society Adam Ferguson treated the growth of civilisation as due to the progressive nature of man, which insists on carrying him forward to limits impossible to ascertain. He formulated the process as a movement from simplicity to complexity, but contributed little to its explanation.] But I will quote one passage from Priestley, the most eminent of the three, and the most enthusiastic for the Progress of man. As the division of labour--the chief principle of organised society--is carried further he anticipates that ... nature, including both its materials and its laws, will be more at our command; men will make their situation in this world abundantly more easy and comfortable; they will probably prolong their existence in it and will grow daily more happy.... Thus, whatever was the beginning of this world, the end will be glorious and paradisiacal beyond what our imaginations can now conceive. Extravagant as some people may suppose these views to be, I think I could show them to be fairly suggested by the true theory of human nature and to arise from the natural course of human affairs.