11 Interaction between the multiplier and accelerator enhances the potential for eco- nomic instability. During expansion, an increase in investment serves to increase con- sumption, which in turn increases the demand for additional investment. Consumption and investment feed each other, and the economy booms. However, full employment places a ceiling on growth and eventually the expansion levels off. The accelerator prin- ciple explains why, as growth and consumption level off, net investment often declines sharply, plunging the economy toward recession.