Unearned increment is an increase in the value of land or any property without expenditure of any kind on the part of the proprietor; it is an early statement of the notion of unearned income. It was coined by John Stuart Mill, who proposed taxing it so that it benefits every member of a society. Mill's concept was refined and developed by nineteenth-century economist Henry George in his book Progress and Poverty (1879). George argued that the value of land increased as population growth expanded the division of labor. A landowner's exclusive claim to their land granted them the ability to collect the excess productivity as economic rent. Thorstein Veblen further developed the concept, pointing out that the value of a piece of land was also dependent on current technological capabilities.