The model states that economic output is a function of money or price "surprise". The model accounts for the empirically based trade off between output and prices represented by the Phillips curve, but the function breaks from the Phillips curve since only unanticipated price level changes lead to changes in output. The model accounts for empirically observed short-run correlations between output and prices, but maintains the neutrality of money (the absence of a price or money supply relationship with output and employment) in the long-run. The policy ineffectiveness proposition extends the model by arguing that, since people with rational expectations cannot be systematically surprised by monetary policy, monetary policy cannot be used to systematically influence the economy.