Government Purchases Line

A representative government purchases line is presented in the exhibit to the right. This red line, labeled G in the exhibit, is positively sloped, indicating that greater levels of income or production generate greater government purchases by the government sector. This positive relation indicates that the government sector, especially state and local governments, is inclined to use increasing tax revenue generated by an expanding economy for government purchases.

The government purchases line graphically illustrates the government purchases-income relation for the government sector, which plays a key role in the aggregate expenditures line used in Keynesian economics to identify equilibrium income and production.

The slope of the government purchases line presented here is positive, but less than one. In fact, the slope of the government purchases line is numerically equal to the marginal propensity for government purchases. In this case the slope is equal to 0.05. The positive slope reflects induced government purchases--more income means more government purchases. Click the [Slope] button to illustrate.

To illustrate the equality between slope and the marginal propensity for government purchases, consider the equations for each. The slope of the government purchases line is specified as the "rise" over the "run." The rise is the change in government purchases measured on the vertical axis and the run is the change in income measured on the horizontal axis.

slope

=

rise run

=

change in government purchases change in income

MPG

=

change in government purchases change in income