The wage-earner, upon change in employment to a better paid job, is unlikely to regard his wage betterment in quite the same way. His bias would be justifiable. He would know of the competition for jobs in his particular vocation and would sense the market forces of supply and demand in operation. The supply of labour for any particular kind of job is strongly influenced in the longer, if not the shorter, run by its transferability from one place to another and by opportunities for education and training. Except in instances where a few, because of the scarcity of their particular abilities and because of the willingness of others to pay for them, are able to maintain abnormally high wage rates, the upward curve of a wage against labour supply is restrained.
Interest rates have comparable limitations.
Demand for the production of goods and services by a consumer population on a fixed total amount of land drives rents upwards by competition towards the best possible use of each site, in equilibrium with rents and usages of all other sites. Interchangeability between one kind of use and another is part of that process. Rent commands the excess of revenue over all labour, capital and entrepreneurial costs. Rent is provided by the increase in productivity of labour and capital, in terms of land area, due to their increased concentration on scarce land. In Ricardian terms, it is provided by the difference between the average productivity of a site and productivity at the margin, external and internal, of production.