Summary: “Twenty Years On: A Survey of the Theory of the Multiplier”

Shackle’s essay is at once a historical commemoration and a conceptual clarification of multiplier theory. Looking back from the early 1950s, he treats Kahn’s 1931 article not as a merely technical footnote to Keynes, but as one of the decisive moments in the formation of modern employment theory.

It is now twenty years since the doctrine of the multiplier was first precisely and explicitly set forth.

The point of the retrospective is that the multiplier’s achievement was precision. Earlier economists and observers could imagine that expenditure might circulate through the economy, but Kahn gave that thought determinate analytical form. Shackle therefore presents originality not as the production of an entirely unprecedented intuition, but as the conversion of a vague and politically urgent idea into a usable instrument for analysing unemployment, public works, saving, investment, and prices.

Kahn’s major innovation, in Shackle’s account, was to shift the question away from an automatic Quantity Theory concern with the general price level and toward the conditions of supply in depression. If unemployed labour and unused capacity exist, additional expenditure need not immediately bid up prices; it may instead call forth additional output and employment. This was what made the public-works problem analytically tractable.

By that simple device Mr Kahn solved the problem of whether and when a policy of public works would cause ‘inflation’, would raise prices, and when not.

Shackle links this insight to several tributaries flowing into Keynes’s General Theory: Kahn’s employment multiplier, Meade’s insistence on the ex post equality of saving and investment, and Warming’s formulation that investment generates the income from which the corresponding saving is made. The multiplier is therefore not simply a chain of spending rounds. It is also a principle of macroeconomic consistency: if investment rises, income must rise sufficiently for saving to match it after the event.

Three at least of the tributary streams of thought which, gaining limpidity upon their way, flowed ultimately into the General Theory, had their source in Mr Kahn’s article.

The elementary multiplier appears as the familiar geometric series: if each increment of income induces a fraction of additional consumption, total income or employment expands by successive rounds. Yet Shackle’s main concern is to prevent that formula from becoming a mechanical slogan. The simplicity of the expression conceals problems of aggregation, distribution, timing, induced investment, and changing expectations.

This is the bare bones of the multiplier principle. Its simplicity and ‘obviousness’ are illusory.

Much of the essay therefore moves from historical reconstruction into methodological critique. Shackle distinguishes received income from expected income, intended saving from realized saving, and planned expenditure from actual outcome. Since individuals do not know one another’s intentions, the multiplier cannot be fully understood as a timeless proportional relation. Consumption may respond to expectations of future income, to wealth, to commitments, or to confidence; the multiplier for a contraction may differ from that for an expansion. These complications make the theory a bridge from Keynesian comparative statics toward a more explicitly uncertain and dynamic economics.

An argument in terms of comparative statics cannot indicate the possibilities discussed above, for by its nature it cannot distinguish meaningfully between past and future, between expectations and intentions on the one hand and outcomes on the other hand.

Shackle’s final concern is the tension between the multiplier as an instantaneous relation and as a process unfolding through time. He argues that these are not necessarily rival doctrines: the first describes possible reactions existing at an instant, while the second describes the realized propagation of effects through credit, belief, recognition, and adjustment. His discussion of Hicks’s trade-cycle theory follows from this point. Hicks gives the multiplier an elegant dynamic role, but at the cost of using a non-expectational mechanism in which consumption depends on past income and uncertainty is deliberately set aside.

The essay’s lasting significance lies in this double movement. It honors Kahn’s multiplier as a foundational device of Keynesian economics, while also exposing the limits of any version that treats it as automatic. For Shackle, the multiplier is most important not as a settled formula but as a problem-opening concept: once time, uncertainty, expectations, and distribution are admitted, it becomes a way of asking how plans become outcomes in a monetary economy.