One of the things that fascinates me in economics is how
different economists manage to come up with completely different conclusions
about the results of particular policy measures. Where this happens, I think it provides an
excellent opportunity to examine how results flow from assumptions and to
appreciate how fragile certain conclusions might be.
One case of this that struck me recently is the New
Keynesian position that a balanced budget increase in public expenditure, which
is expected to be permanent, has no impact on GDP. This result, which contrasts with the old
Keynesian result, is said to be down to the assumption of rational
intertemporally maximising agents. However,
what is perhaps not so well appreciated is that it is also contingent on some
rather ad hoc assumptions about household preferences.
To look at this, I'm going to assume a closed economy with
no investment, so GDP (Y) comprises simply public spending (G) and household
consumption (C) (all in real terms, assuming a single good):
(1) Y = G + C
I'm going to go with the standard assumption that public
spending is funded with lump sum taxes (T).
I don't like this assumption very much, partly because I think it sometimes skews the results, but it makes it easier to be
clear about what constitutes a balance budget change in spending. So household disposable income (YD) is given:
(2) YD = Y  T
Now, in the standard New Keynesian analysis, consumption is
based on lifetime income over an infinite life.
So, if it is assumed that price flexibility will ensure full employment GDP
in the long run, then the permanent increase in taxes will reduce permanent
disposable income. Expected future
consumption will therefore fall and so households will also cut current consumption.
However, this result arises only because of our assumption
about household preferences. We could
take a different approach.
For example, we could assume that household maximise over a finite lifetime. In its simplest form, assume each household lives for two periods and then dies. It works and earns only in the first period but splits its income so as to consume the same amount in each period (so we are assuming, for simplicity, zero elasticity of substitution between consumption in the two periods.) We will also assume an equal number of new households is "born" in every period. Each period, we therefore have half our households spending their savings from the previous period and half spending some fraction of their current earnings. In equilibrium, these households will be saving half their income, so the stock of savings at any time will be equal to 50% of disposable income. [Edit  to clarify, equilibrium here means a steadystate nongrowth equilibrium when prices have been able to fully adjust to remove any output gap.]
For example, we could assume that household maximise over a finite lifetime. In its simplest form, assume each household lives for two periods and then dies. It works and earns only in the first period but splits its income so as to consume the same amount in each period (so we are assuming, for simplicity, zero elasticity of substitution between consumption in the two periods.) We will also assume an equal number of new households is "born" in every period. Each period, we therefore have half our households spending their savings from the previous period and half spending some fraction of their current earnings. In equilibrium, these households will be saving half their income, so the stock of savings at any time will be equal to 50% of disposable income. [Edit  to clarify, equilibrium here means a steadystate nongrowth equilibrium when prices have been able to fully adjust to remove any output gap.]
It will help at this stage to put some numbers on this. I am going to assume that full employment GDP
is 100 and the current real stock of savings is 40. The savings take the form of public debt, but
I am going to assume that public spending and taxes are both currently
zero. Lastly, prices are assumed to be
sticky in the current period and the next, but to be fully flexible thereafter.
So in this instance, we find that expenditure falls short of
what is needed for full employment. The
table below shows the general price level for goods (p), and savings, consumption,
public spending, GDP, taxes and disposable income, all in real terms. In addition to identities (1) and (2), we have the real
value of savings (A) is given as:
(3) A_{t} = (YD_{t1}  Cw_{t1}) / ( p_{t
}/ p_{t1} )
where Cw is workers' consumption. Consumption by retireds is equal to their savings. Workers in one period are retireds in the next, so intertemporal optimising under rational expectations requires that workers' consumption in one period is equal to retireds' consumption in the next.
Period

1

2

3

Price level

1.00

1.00

0.80

Value of savings

40

40

50

Workers' consumption

40

50

50

Retireds' consumption

40

40

50

Public spending

0

0

0

GDP

80

90

100

Taxes

0

0

0

Household disposable income

80

90

100

Each subsequent period will be the same as period 3. So, in this instance, the sticky prices are
creating a temporary shortfall in GDP.
What is the effect of a permanent balanced budget increase in public
spending? This is shown in the table
below.
Period

1

2

3

Price level

1.00

1.00

1.00

Value of savings

40

40

40

Workers' consumption

40

40

40

Retireds' consumption

40

40

40

Public spending

20

20

20

GDP

100

100

100

Taxes

20

20

20

Household disposable income

80

80

80

Again, each subsequent period will be the same as period
3. The effect has been an elimination of
the temporary output gap. The longer run
effect is that the general deflation that occurred in the first example does
not occur here.
It helps to understand what's going on here if you realise
that the assumptions about household preferences imply a steady state ratio
between consumption and the real value of savings. In our example, the output gap arises because
the real value of savings is too low.
GDP is prevented from rising, because if disposable income were to rise,
households would try to save more and with the balanced budget assumption they cannot achieve this. For the same reason, consumption
stays the same when there is a balanced
budget increase in public spending. However,
the fact that there is no price deflation in later periods keeps consumption at
its existing level.
I am not arguing here that one particular assumption about household
preferences is better than the other. I think the latter approach is more consistent with heterodox views, and I find it more plausible, but I suspect what actually happens is much more complicated. All I wanted to do here was illustrate what I thought was an interesting case of where conflicting conclusions arise from different assumptions, even if both involve rational intertemporal maximising agents.
(I should point out that I am aware that the result in my overlapping generation case also depends on how the tax is levied. I have assumed the tax to be paid out of workers' income, but if the retired bear all or some of the burden there is a different result. This is another reason why I am wary of unrealistic assumptions about the structure of taxation.)
(I should point out that I am aware that the result in my overlapping generation case also depends on how the tax is levied. I have assumed the tax to be paid out of workers' income, but if the retired bear all or some of the burden there is a different result. This is another reason why I am wary of unrealistic assumptions about the structure of taxation.)