Ability to Pay The principle that taxes should vary according to an individual's level of wealth or income. Investopedia Says: The application of this principle is a progressive tax system, which is considered to be characteristic of a socialist sentiment. Many hard-line classical economists like Adam Smith believed any elements of socialism would destroy the initiative of the population within a free market economy. However, many countries have blended capitalism and socialism with a great degree of success. Related Terms: Classical Economics Economics Flat Tax Income Tax Invisible Hand Progressive Tax Tax Bracket |