116 THE GENERAL THEORY OF EMPLOYMENT BK. III

stimulated it will be the same as in the other set ofindustries.1 It is easy, indeed, to conceive of cases,as, for example, where the marginal propensity to con-sume is widely different from the average propensity,in which there would be a presumption in favour of

some inequality between ΔYω/ΔN and ΔIω/ΔN2, since there

would be very divergent proportionate changes in thedemands for consumption-goods and investment-goodsrespectively. If we wish to take account of suchpossible differences in the shapes of the relevant por-tions of the aggregate supply functions for the twogroups of industries respectively, there is no difficultyin rewriting the following argument in the moregeneralised form. But to elucidate the ideas involved,it will be convenient to deal with the simplified casewhere k = k'.

It follows, therefore, that, if the consumptionpsychology of the community is such that they willchoose to consume, e.g., nine-tenths of an incrementof income,2 then the multiplier k is 10; and the totalemployment caused by (e.g.) increased public works

1 More precisely, if ee and e'e are the elasticities of employment in industryas a whole and in the investment industries respectively, and if N and N2 arethe numbers of men employed in industry as a whole and in the investmentindustries, we have

ΔYω = Yω/ee . N ΔN

and ΔIω= Iω/e'e . N2 ΔN2'so that ΔN = ee/e'e Iω/N2 N/Yω k . ΔN2'

i.e. k' = Iω/e'eN2 . eeN/Yω k.

If, however, there is no reason to expect any material relevant differencein the shapes of the aggregate supply functions for industry as a whole and

for the investment industries respectively, so that Iω/e'e . N2 = Yω/ee, then it

follows thatΔYω/ΔN= ΔI/ΔN2 and, therefore, that k=k'.

2 Our quantities are measured throughout in terms of wage-units.