In less than two years, negative interest rates have moved from the abstract realms of economic theory into the mainstream of monetary policymaking. The experiment under way in the eurozone, Japan and some smaller European economies has shown that the practical obstacles to taking rates below zero are not as large as once imagined. Proponents say the policy — intended to encourage consumers to spend and banks to lend more to the real economy — has saved the eurozone from sinking into disastrous deflation. But the evidence for this remains tentative. Meanwhile, negative rates are undeniably unpopular, and the longer they remain in place the greater the risk of unintended consequences.

The latest attack on the policy comes from Larry Fink, head of the asset manager BlackRock, who warns of the toll that low, and now negative, rates are taking on savers. People who want a certain income at retirement must now invest far more to achieve it and cut spending accordingly, he argues — making the policy counterproductive.

This could be said of any cut in interest rates, which will always shift income from savers to borrowers. The burden on savers need not outweigh the boost to borrowers simply because interest rates have crossed a psychological threshold at zero.