Logical Identity of Saving and Investment:

J.M. Keynes has put forward two views of saving and investment equality:

(1) Definitional Equality and (2) Functional Equality.

(1) Accounting or Definitional Equality:

According to J.M. Keynes actual saving and actual Investment are always and necessarily equal at any level of income. He writes in his book 'General Theory':

Definition:

"Saving and investment are necessarily equal in amount for the community as a whole, being different aspects of the same thing".

In order to prove it, he defined saving in the current period as the excess of income over expenditure.

Formula For Saving:

S = Y - C

Here, S stands for current saving, Y for current income and C for current consumption.

As regard investment, it is the value of current output of capital goods together with the value of any addition to work in progress or the stock of finished goods. Investment is equal to the output of the community minus consumption.

Formula For Investment:

I = Y - C

Where I stands for investment, Y for income and C for consumption.

Keynesian's Equation For Saving and Investment:

S = Y - C ................... (i)

I = Y - C .................... (ii)

Taking, Y - C is common from both equations (i) and (ii). So we have:

S = I

Saving = Investment

According to the second version of Keynes:

Definition:

"Saving is equal to investment at the equilibrium level of income".

It is brought about by the adjusting mechanism of income compared to the classical view of variations in the rate of interest. Keynes establishes equality between saving and investment by defining income (Y) as equal to current consumption plus current investment.

Y = C + I .................. (i)

Income (Y) is also equal to consumption plus saving.

Y = C + S ................ (ii)

From equations (i) and (ii), we have:

C + I = C + S

C will cancel from both sides of the equation, so:

I = S

 Investment = Saving

The basic idea of explaining equality between saving and investment is that it is brought about by changes in income and not through the mechanism of interest rate.

According to the functional equality version when people save more than what the investors think it worthwhile to invest, the demand for consumer and producer goods falls down. When the goods produced are not profitably sold, the entrepreneurs curtail production of goods and the national income falls. If investment is more than saving, the national income rises. The process of changes is income, saving and investment continues till saving and investment are in equilibrium. The saving and investment equality is explained with the help of a schedule and a curve.

($ in crore)

In the above schedule, it is shown that so long investment is higher than saving, income level continues to rise. When income is $1200 crore, saving and investment are equal to $120 crore each. After this equilibrium point, saving exceeds investment. The equilibrium between saving and investment is reached when income contracts and again reaches $1200 crore. Saving and investment equality is now explained with the help of a curve.

Diagram/Curve/Figure:

In figure (31.1), income is measured on X-axis and saving and investment on Y-axis. SS^/ is the saving curve and II^/ the investment curve. When income is OY^/, the investment is greater than saving, l^/. When investment is more than saving, then income rises. At point L, saving and investment are equal at the equilibrium level of income OY. At point N, saving is greater than investment. The higher saving will bring a fall in income, till the equilibrium is reached at OY, equilibrium income level.

The modem economists make use of functional concepts of saving and investment for emphasizing the behavior of the economy as a whole.