Negative rate: handgun or distress signal?

Summary The negative nominal rates currently enjoyed by some sovereign borrowers, as well as by banks refinancing with central banks that have opted for negative policy rates, have shattered the assumption of a zero floor. Although they extend the room for manoeuvre for monetary policy, are negative rates a deliberate and controlled consequence of crisis management monetary policy or, rather, a symptom of deflation, an indicator of the seriousness of the macroeconomic situation, or even the harbinger of a phenomenon of secular stagnation? Doesn't the recovery depend less on the nominal monetary rate than on the rate of return on productive investment, i.e. the natural rate in Wicksell's sense? This return to the Wicksellian approach to the natural rate of interest leads us to ask whether, in order to ward off the persistent risk of deflation and to postpone the prospect of secular stagnation, it is the monetary rate that we must push ever lower or the natural rate that we must try to raise. In which case, how can the natural rate be raised?