Grasping Reality on TypePad, by Brad DeLong

...It’s about investment slowing down, and none of the normal policy levers being able to speed it up again. What all six of the Smurfs’ explanations have in common is that investment capital, instead of circulating round the economy, gets stuck and starts to pile up somewhere, despite price signals telling it that it ought to be chasing new investments. So any policy response to secular stagnation needs to come up with new ways of persuading investors to invest, ways which aren’t (at least, not in the conventional sense,) price signals.

http://thelongandshort.org/issues/season-three/explaining-secular-stagnation.html