IN THE current literature, comparison continues to be made between the Robertsonian and the Swedish conceptions 2 of sequence analysis and of saving and investment (see, for example, the excellent volume, Survey of Contemporary Economics, edited by Howard S. Ellis). These conceptions appear to be in some manner similar, yet different; but just what is the difference seems to be a somewhat baffling question. To guide the reader, I propose to state certain propositions at the outset: I. The Robertsonian formulation may consist merely of a set of definitions, as presented in his I933 Economic Journal article on Saving and Hoarding (and it is this formulation which Keynes comments upon in the General Theory); second, his period analysis may be presented as a definite formulation of the multiplier sequence over time 3 as is done in his November, I936 Quarterly Journal of Economics review article on Keynes' General Theory. The second formulation makes use of the earlier terminology, but it does not stop with mere definitions; it suggests a definite empirical hypothesis.4 Throughout the following I shall be considering the second formulation, not simply the first. 2. The second Robertsonian formulation is not, as is commonly supposed, a mere tautology. The view that it is such overlooks the third equation referred to below. 3. The Swedish analysis based on the divergence of planned saving and planned investment, as originally interpreted, does not appear to offer a satisfactory theory of income expansion or contraction. 4. Useful analyses can, however, be made in terms of the discrepancy between certain magnitudes, such as the divergence between desired consumption and actual consumption (expenditure-lag) and the divergence between intended investment and actual investment (output-lag). These formulations are often stated in terms which bear some resemblance to, though in fact they are different from, the original Swedish formulation. The expenditure-lag is an integral part of the Robertsonian formulation. And the output-lag 5 (divergence of output from sales) has been employed by Lundberg and Metzler. Both formulations play a significant role in the explanation of the cumulative process. In each case, expansion or contraction will follow as a result of the unsatisfied conditions.