One of Milton Friedman’s most influential and revolutionary theories was his challenge to the traditional Keynesian consumption function, which includes simple after-tax income as a variable in the consumption. Friedman countered, however, that those who consume today take future taxes, price increases, salary increases, and other factors into account. This is summarized in his Permanent Income Hypothesis. More specifically, this counters that people consume based off of their overall estimation of future income as well as opposed to only the current after-tax income.