Gresham’s law needs a corollary. Not only does “bad money drive out good”, but “cheap” money may as well. Ultra low, zero-bounded central bank policy rates might in fact delever instead of relever the financial system, creating contraction instead of expansion in the real economy. Just as Newtonian physics breaks down and Einsteinian concepts prevail at the speed of light, so too might easy money policies fail to stimulate at the zero bound.

Historically, central banks have comfortably relied on a model which dictates that lower and lower yields will stimulate aggregate demand and, in the case of financial markets, drive asset purchases outward on the risk spectrum as investors seek to maintain higher returns. Near zero policy rates and a series of “quantitative easings” have temporarily succeeded in keeping asset markets and real economies afloat in the US, Europe and even Japan. Now, with policy rates at or approaching zero yields and QE facing political limits in almost all developed economies, it is appropriate not only to question the effectiveness of historical conceptual models but to entertain the possibility that they may, counterintuitively, be hazardous to an economy’s health.

Importantly, Gresham’s corollary is not another name for “pushing on a string” or a “liquidity trap”. Both of these concepts depend significantly on perception of increasing risk in credit markets which in turn reduce the incentive of lenders to expand credit. Rates at the zero bound do something more. Zero-bound money – credit quality aside – creates no incentive to expand it. Will Rogers once fondly said in the Depression that he was more concerned about the return of his money than the return on his money. But from a system-wide perspective, when the return on money becomes close to zero in nominal terms and substantially negative in real terms, then normal functionality may break down.