A Keynesian model of the macroeconomy that includes the two private sectors, the household sector and the business sector. This Keynesian model variation, often termed the basic Keynesian model or the private sector Keynesian model, captures the interaction between induced consumption expenditures and autonomous investment expenditures. This model is commonly used to illustrate the basic workings of Keynesian economics, including equilibrium, disequilibrium, and the multiplier. Equilibrium is identified as the intersection between the C + I line and the 45-degree line. Two related variations are the three-sector Keynesian model and the four-sector Keynesian model.