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利子率がある水準まで低下すると、たいていの人々が利子率のきわめて低い債権を保有するよりも現金のほうを選好するようになるという意味で、流動性選好が事実上無制限になる可能性がある。このような事態に陥ると、通貨当局は利子率を有効に制御する手立てを失ったも同然である。もっともこの極限的な場合は、将来ならいざ知らず将来には現実にも重要になるかもしれないこれまでのところは、そのような例を聞いたことがない。実際、たいていの通貨当局は長期債権の売買になかなか踏み切れないから、〔この極限の場合を実地に〕検証する機会はあまりなかった。そもそもこのような事態が出来したとしたら、そのときには、公共当局自身が銀行体系を通じ、名ばかりの金利でいくらでも借入れができることになろう。
28 The IS-LM Framework
449
The LM curve
Figure 28.4
(a)
(b)
Interest
rate
(L(i Y)
LiY
L (iY.)
Interest
LM curve
ra
B
A
Y2 Income (Y)
Money demand and supply
Each point in the income-interest space is consistent with money market equilibrium. This set of points is the
LM curve.
Note that at interest rate, i, the LM curve is flat. What does that mean? The horizontal segment of the LM
curve relates to the presence of the liquidity trap. The liquidity trap arises at some minimum interest rate (which
could be zero) where everybody forms the view that the only direction for interest rates is up. The equivalent
expectation is that everybody considers that capital losses will be incurred on bond portfolios because when
interest rates rise, bond prices fall. The result is that once interest rates reach this minimum level, all people will
prefer to hold any new money in the form of cash instead of bonds
Keynes said (1936: 207):
There is the possibility... that, after the rate of interest has fallen to a certain level, liquidity-preference may
become virtually absolute in the sense that almost everyone prefers cash to holding a debt which yields so low
a rate of interest. In this event the monetary authority would have lost effective control over the rate of
interest.. Moreover, if such a situation were to arise, it would mean that the public authority itself could borrow
through the banking system on an unlimited scale at a nominal rate of interest.
As we will see when we consider policy analysis within the IS-LM framework, the existence of a liquidity trap ren-
ders monetary policy ineffective as a stabilisation tool at low interest rates
Monetary policy is characterised in this IS-LM framework as the central bank manipulating the money supply.
When the interest rate is at i in Figure 28.4, increasing the money supply would have no impact on interest rates
or the price of bonds. In other words, monetary policy changes cannot alter the level of national income.
In a liquidity trap, a rise in the money supply leads to an equal rise in the demand for money and as a result the
interest rate does not change. We will consider this in more detail later in the chapter.
The LM curve is upward sloping at higher levels of income because as national income rises, the demand for
money increases and at each given money supply, the interest rate has to rise to ration the excess money demand
and maintain money market equilibrium.
The slope of the LM curve is steeper:
The more sensitive the demand for money (transactions and precautionary motives) is to national inco
changes. Thus, small increases in national income lead to large changes in excess money demand for a giv
posted by yoji at 7:04 午後
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