One common explanation is that in anticipation of falling prices, consumers delay purchases, causing them to fall still further. This argument is a simplification; it can be made with equal power in reverse to argue that inflation will inevitably run upwards as consumers bring purchases forward to avoid being stung later. But the argument hints at the right problem: deflation’s effect on interest rates. Generally speaking, the interest rate reflects the price of consumption today relative to consumption tomorrow. When interest rates are high, savings are worth more tomorrow, and vice-versa. The return in money terms (the rate advertised by banks) is called the “nominal” interest rate. But inflation also matters. Subtracting expected inflation from the nominal rate produces the real interest rate—the expected return after inflation—which is what people respond to in most models of the economy.