Stock market booms, endogenous credit creation and the implications of broad and narrow banking for macroeconomic stability

In this paper we study the implications of the present broad banking system for macroeconomic stability. We show that when commercial banks are allowed to trade in financial assets (here equities) as a substitute for traditional lending, the macroeconomic system is likely to be an unstable one. We then consider a narrow banking system defined by a Fisherian 100 percent reserve ratio for checkable deposits and the ban for commercial banks from trading in stocks and other financial assets. Within the stylized theoretical framework set up here, we show that in the second system macroeconomic stability is guaranteed by some weak assumptions on the behavior of economic agents. Moreover, while a sufficient loan supply can be guaranteed in such a framework, the rationale for bank runs can be eliminated, in contrast to what is likely to happen under traditional broad banking. Though narrow banking is an extreme banking system unlikely to be adopted in the short-run, its features highlight the stability and efficiency properties that the separation between commercial and investment banking bring about.