I once made the [blindingly naive] observation that in a capitalist system there should is no idle money. After all even savings placed with a banking institution isn’t “left” sitting in an account but rather is turned around in the form of loans to other bank customers. Even on its face this is false since every bank has reserve requirements. There has to be a a good way of measuring the quantity or at least proportion of idle money and then measuring this against various metrics of economic performance. Is there a general optimal level of idle money? I suppose this presumes, among other things, a firm definition of “idle” money.