Larry Summers explains his secular stagnation hypothesis in Vox: If the full employment real rate of interest (FERIR) is low and so is inflation, full employment may be out of reach. Price rigidities may amplify the effect if they induce expectations of falling prices. In addition, low interest rates tend to undermine financial stability, by fostering an aggressive search for yield and Ponzi schemes. Several factors suggest that the FERIR has been falling. Summers proposes to operate under a higher inflation rate target and to spend more on public investment.