Investment Line

A representative investment line is presented in the exhibit to the right. This red line, labeled I in the exhibit, is positively sloped, indicating that greater levels of income generate greater investment by the business sector. This positive relation indicates that the business sector is inclined to divert higher profits generated by an expanding economy to investment expenditures on capital goods.

The investment line graphically illustrates the investment-income relation for the business sector, which is then added to the consumption line to derive the aggregate expenditures line used in Keynesian economics to identify equilibrium income and production.

The intercept of the investment line indicates the intersection point between the investment line and the vertical investment axis. The investment line intersects the vertical axis at a value of $2 trillion. Theoretically, this is a minimum "baseline" level of investment, the amount of investment undertaken if income falls to zero. This intersection indicates autonomous investment--investment unrelated to income. Click the [Intercept] button to illustrate.

Autonomous investment is investment by the business sector that is unrelated to and unaffected by the level of income or production. This is best indicated by a zero level of income. While individual businesses occasionally come face-to-face with autonomous investment, as their own slice of aggregate income drops to zero, for the aggregate economy autonomous investment is mostly an unlikely theoretical extrapolation.