Friedman's challenges to what he later called "naive Keynesian" (as opposed to New Keynesian) theory[4] began with his 1950s reinterpretation of the consumption function, and he became the main advocate opposing Keynesian government policies.[5] In the late 1960s, he described his own approach (along with all of mainstream economics) as using "Keynesian language and apparatus" yet rejecting its "initial" conclusions.[6]