178 THE GENERAL THEORY OF EMPLOYMENT BK. IV

although he did not expressly say so, that aggregatesaving and aggregate investment are necessarily equal.Indeed, most members of the classical school carried thisbelief much too far; since they held that every act of in-creased saving by an individual necessarily brings intoexistence a corresponding act of increased investment.Nor is there any material difference, relevant in this con-text, between my schedule of the marginal efficiency ofcapital or investment demand-schedule and the demandcurve for capital contemplated by some of the classicalwriters who have been quoted above. When we cometo the propensity to consume and its corollary the pro-pensity to save, we are nearer to a difference of opinion,owing to the emphasis which they have placed on theinfluence of the rate of interest on the propensity tosave. But they would, presumably, not wish to denythat the level of income also has an important influenceon the amount saved; whilst I, for my part, would notdeny that the rate of interest may perhaps have aninfluence (though perhaps not of the kind which theysuppose) on the amount saved out of a given income.All these points of agreement can be summed up in aproposition which the classical school would acceptand I should not dispute; namely, that, if the levelof income is assumed to be given, we can infer thatthe current rate of interest must lie at the point wherethe demand curve for capital corresponding to differentrates of interest cuts the curve of the amounts savedout of the given income corresponding to different ratesof interest.

But this is the point at which definite error creepsinto the classical theory. If the classical school merelyinferred from the above proposition that, given thedemand curve for capital and the influence of changesin the rate of interest on the readiness to save out ofgiven incomes, the level of income and the rate ofinterest must be uniquely correlated, there would benothing to quarrel with. Moreover, this proposition