Marginalism is a theory of economics that attempts to explain the discrepancy in the value of goods and services by reference to their secondary, or marginal, utility. The reason why the price of diamonds is higher than that of water, for example, owes to the greater additional satisfaction of the diamonds over the water. Thus, while the water has greater total utility, the diamond has greater marginal utility. The theory has been used in order to explain the difference in wages among essential and non-essential services, such as why the wages of an air-conditioner repairman exceed those of a childcare worker.