The article discusses two types of economic models used before and after the 1970s. Before 1970, most models focused on demand changes affecting output and employment. However, these models faced challenges due to theoretical and empirical reasons. The traditional Keynesian model, which emphasized fixed prices, could not explain the rising inflation and unemployment rates in the 1970s. This led to a reevaluation of the existing economic theories and the need for new models to better understand and predict economic fluctuations.