Ironically, mainstream economics has taken the "purposeful behavior" idea very seriously. Models almost entirely consist of agents acting purposefully. If age

Ironically, mainstream economics has taken the "purposeful behavior" idea very seriously. Models almost entirely consist of agents acting purposefully. If agents are smart and prices are set by supply and demand, then money doesn't have real effects and a pure quantity theory of money holds. If agents are dumb, then you get mispricing but markets still clear and you don't get unemployment or factories closing. If prices are sticky, then it doesn't matter if agents are smart or dumb -- you get recessions that last unnaturally long unless either the government or the central bank steps in. So New Keynesianism is completely compatible with "human action is purposeful behavior". But still, the rest of us prefer to test our theories by looking at evidence.