(1)(1)
(2)(2)
Jordi gali 2008 monetary policy, inflation and the business cycle
chapter 2 A classical monetary model
this chapeter presents a simple model of a classical monetary economy,
fearturing perfect competition and fully flexible prices in all markets.
as stressde below,many of the predictions of classical economy are strongly at
odds with the evidence reviewed in chapter 1.that notwithstanding, the analysis
of the calssical economy provides a benchmark that will br useful in subsequent
chapters when some of its strong assumptions are relex.
the proposed framework assumes a representative agent solving a dynamic
optimization problem.
2.1 households
the representative household seeks to maximize the objective function
E
0>t = 0
N
βtU C
t
, N
t
E
0
>
t = 0
N
βt U C
t
, N
t
Nt denotes hours of work or employment. the period utility function U Ct , Nt
is assumed to be continuous and twice diferentiable, with
vU
v C
t
O0 ,
v
2U
v Ct
2 # 0 ,
vU
v N
t
! 0,
v
2U
v Nt
2 #0
maximazation (1) is subject to a sequence of flow budget constraints given
by
P
t
$C
t
CQ
t
$B
t
#B
tK1
CW
t
N
t
KT
t
P
t
C
t
CQ
t
B
t
%B
tK1
CW
t
N
t
KT
t
Bt represent the quantity of one-period, nominally riskless discount bonds
purchased in periond t and maturing in period t+1. each bond pays one unit
of money at maturity and its price is Qt. Tt represent lump‐sum additions or
subtractions to period income(e.g.,lump‐sum taxes,dividends,etc.), expressed in
nominal term.
when solvling the problem above, the household is assumed to taken as given the
prices of the good, the wage, and the prices of bonds.
(3)(3)
(4)(4)
(5)(5)
a solvencyconstraint that prevents it from engaging in ponzi‐type schemes
lim
T /N
E
t
B
t
P 0
0% Et Bt
optimal consumption and labor supply
optimal conditions implied by (1) subject to (2) are given by
K
U
n, t
U
c, t
=
W
t
P
t
K
Un, t
Uc, t
= WtPt
Q
t
= β$E
t
U
c, tC1
U
c, t
$
P
t
P
tC1
Qt = β Et
Uc, tC1 Pt
Uc, t PtC1
explanation for (5):
consider the impact on expected utility as of time t of allocation of
consumption betweent time t and time t+1, while keeping consumption in
any periond other than t and t+1 , and hours worked(in all perionds)
unchanged. if the househole is optimizing, it must be the case that
U
c, t
$dC
t
CβE
t
U
c, tC1
$dC
tC1
= 0
for any pairs of (dC
t
, dC
tC1
) satisfying
P
tC1
$dC
tC1
=K
P
t
Q
t
$dC
t
,this eauqtion determines the increases in
consumption expenditures in periond t+1 made possible by the additional
savings KP
t
$dC
t
allocated into one‐periond bonds.
combining the two previous equations yields the intertemporal optimal
condition (5).
assumes that the periond utility takes the form
(8)(8)
(7)(7)
(6)(6)
U C
t
, N
t
=
Ct
1Kσ
1Kσ K
Nt
1C4
1C4
the consumer's optimality conditons (4) and (5) thus become
W
t
P
t
= C
t
σ
$N4
t
Wt
Pt
= Ct
σ Nt4
Q
t
= β$E
t
C
tC1
C
t
Kσ
$P
t
P
tC1
Qt = β Et
CtC1
Ct
Kσ
Pt
PtC1
note for the future reference ,the equation (6) can be rewritten in log‐linear
form as
w
t
Kp
t
= σ$c
t
C4$n
t
wtKpt = σ ctC4 nt
the previous contion can be viewed as a competitive labor market supply
schedule, determing the quantity of labor supplied as a function of real wage,
given the marginal utility of consumption(which under the assumptions is a
function of sonsumption only).
log-linear approximation of (7)
the consumer's Euler equation (7) can be rewritten as
1 = E
t
exp i
t
Kσ$Δc
tC1
Kπ
tC1
Kρ
where
i
t
=KlogQ
t
, ρ =Klogβ , π
tC1
= p
tC1
Kp
t
is the rate of inflation betweent t and t
C1 having defined p
t
= logP
t
.
in a perfect foresight steady state with constant inflation π and constant
growth Y
(10)(10)
(9)(9)
i=ρ+π+σY ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐(why?)
with the steady state real rate given by
r=i‐π=ρ+σY
A first‐order taylor expansion of exp i
t
Kσ$Δc
tC1
Kπ
tC1
Kρ around that
steady state yields
exp i
t
Kσ$Δc
tC1
Kπ
tC1
Kρ x 1C i
t
K i Kσ$ Δc
tC1
KY K π
tC1
Kπ = 1C i
t
Kσ$Δc
tC1
Kπ
tC1
Kρ
then we get the log‐linearized Euler equation
c
t
= E
t
c
tC1
K
1
σ itKEt πtC1 Kρ
a log‐lineat approximation of (7) around a steady state with constant rates of
inflation and consumption growth (i,π,Y) is given by
c
t
= E
t
c
tC1
K
1
σ itKEt πtC1 Kρ
ct = Et ctC1 K
itKEt πtC1 Kρ
σ
where
i
t
=KlogQ
t
, ρ =Klogβ , π
tC1
= p
tC1
Kp
t
is the rate of inflation betweent t and t
C1 having defined p
t
= logP
t
.
note that i
t
corresponds to the log of gross yields on the one period bond.
henceforth, it is referred to as the nominal interste rate.
similarly , ρ can be interpreted as the household's dicount rate.
while the previous frame work does not explicitly introduce a motive for holding
money balances, in some cases it will be convenient to postulate a demand for
real balances with a log‐linear form given by
m
t
Kp
t
= y
t
Kη$i
t
mtKpt = ytKη it
where ηP0 denotes the interest semi‐elasticity of money demand.
a money demand equation similar to (10) can be derived under a variety of
assumptions. for instance, it can be derived as an optimality condition for the
household when money balances yields utility.
(13)(13)
(12)(12)
(14)(14)
(11)(11)
2.2 firm
a representative firm is assumed whose technology is described by a production
function given by
Y
t
= A
t
$N
t
1Kα
Yt = At Nt
1Kα
where A represents the technology level , and a
t
= logA
t
evolves exogenously
according to some stochastic process.
each period the firm maximizes prodits
P
t
$Y
t
KW
t
$N
t
Pt YtKWt Nt
subject to (11), taking the price and wage as given.
maximization of (12) subject to (11) yields the optimality conditon
W
t
P
t
= 1Kα $A
t
$N
t
Kα
Wt
Pt
= 1Kα At NtKα
i.e. the firm hires labor up to the point where its marginal product equals the real
wage.
equivalently, the marginal cost
W
t
1Kα $A
t
$Nt
Kα must be equated to the price Pt
in log‐linear terms,
w
t
Kp
t
= α
t
Kα$n
t
Clog 1Kα
wtKpt = αtKα ntCln 1Kα
which can be interpreted as labor demand schedule, mapping the real wage into
the quantity of labor demanded, given the level of technology.
2.3 equilibrium
the baseline model abstracts from aggregate demand components like
investment, government purchases, or net exports.
(17)(17)
(15)(15)
(18)(18)
(16)(16)
(19)(19)
accordingly,the goods market clearing conditon is given by
y
t
= c
t
yt = ct
i.e., all output must be comsumed.
by combining the optimality conditons of households (8) and firms with (14) and
(15) and the log‐linear aggregate production relationship
y
t
= α
t
C 1Kα $n
t
yt = αtC 1Kα nt
the equilibrium levels of employment and output are determined as a function of
the level of technology
n
t
=K
Kσ α
t
Cα
t
Cln 1Kα
KαKσCσ αK4
nt =K
Kσ αtCαtCln 1Kα
KαKσCσ αK4
y
t
=
Kα
t
4Kα
t
K ln 1Kα Cα ln 1Kα
KαKσCσ αK4
yt =
Kαt 4KαtKln 1Kα Cα ln 1Kα
KαKσCσ αK4
further more, given the equilibrium process for output,(9) can be used to
determine the inplied real rate,
as we know in the log‐lineat approximation of (7)
r=i‐π=ρ+σY
r
t
= ρCσ$E
t
Δy
tC1
= ρCσ$
K 4C1 E
t
α
tC1
KαKσCσ αK4
finally ,the equilibrium real wage ω
t
=w
t
Kp
t
is given by
ω
t
= α
t
Kα$n
t
C log 1Kα
ωt = αtKα ntCln 1Kα
so
ω
t
= α
t
Kα$K
Kσ α
t
Cα
t
Cln 1Kα
KαKσCσ αK4 Clog 1Kα
if we define
ψ
nα=
1Kσ
σ$ 1Kα C4Cα , wn =
log 1Kα
σ$ 1Kα C4Cα ,
ψ
yα=
1C4
σ$ 1Kα C4Cα , wy =
1Kα $log 1Kα
σ$ 1Kα C4Cα = 1Kα $wn ,
ψ
wα =
σC4
σ$ 1Kα C4Cα , ww =
σ$ 1Kα C4 $log 1Kα
σ$ 1Kα C4Cα ,
then we can get
n
t
= ψ
nααtCwn
y
t
=ψ
yααtCwy
r
t
= ρCσ$ψ
yα$Et ΔαtC1
ω
t
= ψωααtCww
notice that the equilibrium dynamics of employment, output, and the real interest
rate are determined independently of monetary policy.
in other words, monetary policy is neutral with respect to those real variables. in
the simple model, output and employment fluctuate in response to variations in
technology, which is assunmed to be the only real driving force.
in particular,output always rises in the face of technology incease, with the size of
increase being given by ψ
yαO 0 ,the same is true for the real wage.
on the other hand, the sign of employment is ambiguous, depending on wether σ
(which measure the strength of the wealth effect of labor supply) is larger or
smaller than one. when σ<1, the substitution effecton labor supply resulting from
a higher real wage doninates the negative effect caused by a smaller marginal
utility of consumption, leading to an increase in employment.the converse is true
when σ>1.
when σ=1 the utility of consumption is logarithmic, employment remains
unchanged in the face of technology variations, for substituion effect and wealthe
effect exactly cancel one anbother.
finally the response of the real real interst rate depends crucially on the time series
properties of technology. if the current improvement in technology is transitory so
that
(21)(21)
(20)(20)
E
t
α
tC1
!α
t
,then the real rate will go down. otherwise, if technology is
expected to keep improving, then E
t
α
tC1
Oα
t
,and the real interest rate will
increase with a rise in α
t
.
what about nominal variables, like inflation or nominal interest rate? not
surprisingly, and in contrast with real variables, their equilibrium bebavior cannot
be determined uniquely by real foeces.
instead, it requires the specification of how monetary policy is conducted. several
monetary policy rules and their implied outcomes will be considered next.
1C1 = 2
2 = 2
2.4 monetary policy and price level determination
let us start by examining the implications of some interest rate rules.
rules that invovle monetary aggregates will be introduced later.
all cases will make use of the Fisherian equation
i
t
= E
t
π
tC1
Cr
t
it = Et πtC1 Crt
2.4.1 an exogenous path for the nominal interest rate
assumes nominal interest rate following an exgenous stationary process i
t
,
and has mean ρ, which is consistent with a steady state with a zero inflation
and no secular growth.
using (21) ,write
E
t
π
tC1
= i
t
Kr
t
note that expectation is pinned down by the previous equation but actual
inflation is not. because there is no other condition that can be used to
determine inflation, it follows that any path for the prices level that satisfies
p
tC1
= p
t
C i
t
Kr
t
Cξ
tC1
is consistent with equilibrium, where ξ
tC1
is a shock, possibly unrelated to
economic fundamentals, satisfying E ξ
tC1
= 0 for all t.
an equilibrium in which such nonfundamental factors may cause fluctuations in
one or more variables is referred to as an indeterminate equilibrium. the
(22)(22)
(23)(23)
example above shows how an exogenous nominal interest rate leads to price
level indeterminacy.
notice that when (10) is operative the equilibrium path for the money supply
(which is endogenous under the present regime) is given by
m
t
= p
t
Cy
t
Kη$i
t
hence , the monetary supply will inherit the indeterminacy of p. the same will
be true of the nominal wage.
2.4.2 a simple inflation-based interest rate rule
suppose that the central bank adjust the interest rate according to the rule
i
t
= ρCφπ$πt
where φ>0.
combining the previous rule with the fisherian equation (21) yields
φπ$πt = Et πtC1 Crt
^
φπ πt = Et πtC1 Crˆt
wherert
^hr
t
Kρ
if φπO 1, the previous difference equation has only one stationary solution, i.e.,
a solution that remains in the neighborhood of the steady state. that solution
can be obtained by solving (22) forward, which yields
π
t
=>
k = 0
N
φπ
K kC1
$E
t
r
tCk
^ -------------------------------------------
---------------------------------------(23)
1 = 1
1 = 1
the previous equation fully ditermines inflation(and ,hence, the price level) as a
function of the path of the real rate ,which in turn is a function of fundamentals.
consider, for the sake of illustration, tha case in which technology follows the
stationary AR(1) process
α
t
= ρα$αtK1Cεt
α
, where ρα2 0, 1
then rt
^ = r
t
Kρ = ρCσ$ψ
yα$Et ΔαtC1 Kρ =Kσ$ψyα 1Kρα $αt
(24)(24)
which combined with (23) yields the following expression for equilibrium
inflation
π
t
=K
σ$ψ
yα$ 1Kρα
φπKρα
$α
t
note that a central bank following a rule of the form considered here can
influence the degree of inflaion by choosing the size of φπ
the larger is the latter parameter the smaller will be the impact of the real
shock on inflation.
if φπ! 1, the stationary solution to (22) take the form
π
tC1
= φπ$πtKrt
^
Cξ
tC1
πtC1 = φπ πtKrˆtCξtC1
where ξ
t
is ,again , an arbitrary sequence of shocks, possibly unrelated to
fundamentals, satisfying E
t
ξ
tC1
= 0, for all t.
accordingly, any process satisfying (24) is consistent with quilibrium, while
remaining in a neighborhood of the steady state. so, as in the case of an
exgonous nominal rate, the price level( and ,hence, inflation and the nominal
rate) are not determined uniquely when the interest rate rule implies a weak
response of the nominal rate to change in inflation.
more specifucally, the condition for a determined price level, φπO 1, requires
that the central bank adjust nominal rate more than one for one in response to
any change in inflation, a property known as taylor principle.
the previous result can be viewed as a particular instance of the need to satisfy
the taylor principle in order for an interest rate rule to bring about a determined
equilibrium.
2.4.3an exogenous path for the money supply
suppose that central bank sets an exponous path for the money supply m
t
.
using (10) to eliminate the nominal interest rate in (21), the following difference
equation for the price level can be derived as
p
t
=
Ky
t
Cη$ E
t
$ p
tC1
Cη$ r
t
Cm
t
ηC1
or rearranged as
(25)(25)
p
t
=
η
1Cη $Et ptC1 C
1
1Cη $mtCut , where ut
=
η$r
t
Ky
y
1Cη envolves independently of mt .
assuming η>0 and solving forward obtains
p
t
=
1
1Cη$>k = 0
N η
1Cη
k
$E
t
m
tCk
Cu'
t
, where u'
t
=>
k = 0
N η
1Cη
k
$E
t
u
tCk
is again, independent of monetary policy.
equicalently, the previous expression can be rewritten in terms of expected
future growth rate of money as
p
t
=m
t
C>
k = 1
N η
1Cη
k
$E
t
Δm
tCk
Cu'
t
25 = 25
25 = 25
hence , an arbitrary exgonous path for the money supply always determines
the price level uniquely.
given the price level, as described above, (10) can be used to solve for the
nominal interest rate
i
t
= ηK1 y
t
K m
t
Kp
t
= ηK1>
k = 1
N η
1Cη
k
$E
t
Δm
tCk
Cu''
t
where u''
t
hηK1 u'
t
Cy
t
is independent of monetary policy.
for example, consider the case in which money growth follows the AR(1)
process
Δm
t
= ρ
m
$Δm
tK1
Cεt
m
for simplicity, assume the absence of real shocks, thus implying a constant
output and a constant real rate. without loss of generality, set r
t
= y
t
= 0 for all t.
then, it follows from (25) that
p
t
=m
t
C
η$ρ
m
1Cη$ 1Kρ
m
$Δm
t
hence , in response to an exgonous monetary policy shock, and as long as
ρ
m
O 0,(the relevant case, given the observed positive autocorrelation of
monetary growth), the price level should respond more than one for one with
the increase in the money supply, a prediction that contrast starkly with the
sluggish response of the price level observed in empirical estimates of the
effects of monetary policy shocks as discussed in chapter 1.
the nominal interest rate is in turn given by
i
t
=
ρ
m
1Cη$ 1Kρ
m
$Δm
t
i.e., in response to an expansion of the monetary supply, and as long as ρ
m
O0,
the nominal interest rate is predicted to go up.
in other words, the model implies the absence of a liquidity efect, incontrast
with the evidence discussed in chapter 1.
2.4.4 optimal monetary plicy
The analysis of the baseline classical economy above has shown that while real
variables are independent of monetary policy, the latter can have important
implications for the behavior of nominal variables and, in particular, of prices.
Yet, and given that the household’s utility is a function of consumption and
hours only— two real variables that are invariant to the way monetary
policy is conducted—it follows that there is no policy rule that is better than
any other. Thus, in the classical
model above, a policy that generates large fluctuations in inflation and other
nominal variables (perhaps as a consequence of following a policy rule that
does not guarantee a unique equilibrium for those variables) is no less desirable
than one that succeeds in stabilizing prices in the face of the same shocks.
The previous result, which is clearly extreme and empirically unappealing, can
be overcome once versions of the classical monetary model are considered
in which a motive to keep part of a household’s wealth in the form of
monetary assets is introduced explicitly. Section 2.5 discusses one such
model in which real balances are assumed to yield utility.
The overall assessment of the classical monetary model as a framework to
understand the joint behavior of nominal and real variables and their
connection to monetary policy cannot be positive. The model cannot explain
the observed real effects of monetary policy on real variables. Its predictions
regarding the response of the price level, the nominal rate, and the money
supply to
(26)(26)
exogenous monetary policy shocks are also in conflict with the empirical
evidence.
Those empirical failures are the main motivation behind the introduction of
nominal frictions in otherwise similar models, a task that will be undertaken in
chapter 3.
2.5 money in utility function
In the model developed in the previous sections, and in much of the recent
monetary literature, the only role played by money is to serve as a numéraire, i.e.,
a unit of account in which prices, wages, and securities’ payoffs are stated.
Economies with that characteristic are often referred to as cashless economies.
Whenever a simple log‐linear money demand function was postulated, it was
done in an adhoc manner without an explicit justification for why agents
would want to hold an asset that is dominated in return by bonds while having
identical risk properties.
Even though in the analysis of subsequent chapters the assumption of a cashless
economy is held, it is useful to understand how the basic framework can
incorporate a role for money other than that of a unit of account and, in particular,
how it can generate a demand for money. The discussion in this section focuses
on models that achieve the previous objective by assuming that real balances are
an
argument of the utility function.
The introduction of money in the utility function requires modifying the
household’s problem in two ways. First, preferences are now given by
E
0>t = 0
N
βtU C
t
,
M
t
P
t
, N
t
E0 >t = 0
N
βt U Ct,
Mt
Pt
, Nt
Second, the flowbudget constraint incorporates monetary holdings explicitly,
taking the form
P
t
C
t
CQ
t
B
t
CM
t
%B
tK1
CM
tK1
CW
t
N
t
KT
t
(27)(27)
(28)(28)
By letting A
t
hB
tK1
CM
tK1
denote total financial wealth at the beginning of the
period t (i.e., before consumption and portfolio decisions are made), the previous
flow budget constraint can be rewritten as
P
t
C
t
CQ
t
AtC1C 1KQt $Mt%AtCWt NtKTt
Pt CtCQt AtC1C 1KQt Mt%AtCWt NtKTt
with the solvency constraint now taking the form
lim
t /N
E
t
At P0, for all t.
The previous representation of the budget constraint can be thought of as
equivalent to that of an economy in which all financial assets (represented by At )
yield a gross nominal return Qt
K1 = exp Ki
t
, and where agents can purchase
the utility yielding “services” of money balances at a unit price
1KQ
t
= 1Kexp Ki
t
x i
t
. Thus, the implicit price for money services roughly
corresponds to the nominal interest rate, which in turn is the opp