A random‐matching model of money is used to deduce the effects of a once‐for‐all change in the quantity of money. It is shown that the change has short‐run effects that are predominantly real and long‐run effects that are in the direction of being predominantly nominal provided that the change is random and people learn its realization only with a lag. The change in the quantity of money comes about through a random process of discovery that does not permit anyone to deduce the aggregate amount discovered when the change actually occurs.