My point here is not to disregard the complex interaction between demand and supply factors, and the possibility that hysteresis has contributed to the post-crisis slowdown in output growth.10 And as I said, fiscal policy should contribute where it is available.
But I want to stress that we need to enhance our understanding of the supply side so we can better appreciate its interactions with demand. For instance, we know too little about which policies  5  See Summers, L. (2015), “Rethinking Secular Stagnation After Seventeen Months.” IMF Rethinking Macro III Conference, 16 April. 6  See Cœuré, B.