JOURNAL OF ECONOMIC THEORY 7,
53-65 (1974)
Uniqueness of the Price Level in
Monetary Growth Models with
Rational
FISCHER BLACK*
Graduate School of Business,
Uhevsity of Chicago, Chicago, Illinois 60637
Received September 11, 1972
INTRODUCTION
Almost every model of a monetary economy
assumes that individuals
and firms behave irrationally.
They buy and sell goods at prices other than
equilibrium prices, or they count
the money the government gives them as
wealth but ignore the fact that
everyone else is getting money Tao, or they
continue to expect zero inflation
when the rate of inflation has been increasing
for several periods. Monetary
growth models1 have moved in the
direction of assuming rational
behavior, but they have generally continued
to assume that expectations about
the rate of inflation are formed in an
irrational manner. Following
Cagan [4], they typically assume some form
of adaptive expectations, even
when some other rule for revising expectations
would give more accurate results.
In a model that does not include
uncertainty in some explicit form, a
straightforward way to put in
rational expectations is to assume that
individuals and firms have
perfect foresight. One can then look at the set
of paths for all economic
variables such that each individual is maximizing
his utility and each firm is
maximizing its value, at every point in time, in
the light of the current and
future values of all the variables. Each such
path is a “competitive
equilibrium” consistent with rational economic
behavior.2
In a world with well-developed
financial markets, it is not easy to
describe a mechanism by which
changes in monetary policy or changes in
the money supply itself will lead
to changes in the price Level or rate of
* I am grateful to William Brock,
Stanley Fischer, Milton Friedman, Arthur Laffer,
Merton Miller, David Ranson,
Thomas Sargent, Charles Upton, and a referee for ideas
and comments on earlier drafts.
Special thanks go to William Brock.
1 For example, see Sidrauski
[13].
* This approach has been
developed most completely by Brock [Zj.
53
Copyright 0 1974 by Academic
Press, Inc.
All rights of reproduction in any form reserved.