Keynesian economics ( KAYN-zee-?n; or Keynesianism) comprises various macroeconomic theories about how in the short run - and especially during recessions - economic output is strongly influenced by aggregate demand (total spending in the economy). In the Keynesian view, aggregate demand does not necessarily equal the productive capacity of the economy; instead, it is influenced by a host of factors and sometimes behaves erratically, affecting production, employment, and inflation.
The theories forming the basis of Keynesian economics were first presented by the British economist John Maynard Keynes during the Great Depression in his 1936 book, The General Theory of Employment, Interest and Money. Keynes contrasted his approach to the aggregate supply-focused classical economics that preceded his book. The interpretations of Keynes that followed are contentious and several schools of economic thought claim his legacy.
Keynesian economists generally argue that, as aggregate demand is volatile and unstable, a market economy will often experience inefficient macroeconomic outcomes in the form of economic recessions (when demand is low) and inflation (when demand is high). These can be mitigated by economic policy responses, in particular, monetary policy actions by the central bank and fiscal policy actions by the government, which can help stabilize output over the business cycle. Keynesian economists generally advocate a managed market economy - predominantly private sector, but with an active role for government intervention during recessions and depressions.
Keynesian economics served as the standard economic model in the developed nations during the later part of the Great Depression, World War II, and the post-war economic expansion (1945-1973), though it lost some influence following the oil shock and resulting stagflation of the 1970s. The advent of the financial crisis of 2007-08 caused a resurgence in Keynesian thought, which continues as new Keynesian economics.
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At the time that Keynes's wrote the General Theory, it had been a tenet of mainstream economic thought that the economy would automatically revert to a state of general equilibrium: it had been assumed that, because the needs of consumers are always greater than the capacity of the producers to satisfy those needs, everything that is produced would eventually be consumed once the appropriate price was found for it. This perception is reflected in Say's law and in the writing of David Ricardo, which state that individuals produce so that they can either consume what they have manufactured or sell their output so that they can buy someone else's output. This argument rests upon the assumption that if a surplus of goods or services exists, they would naturally drop in price to the point where they would be consumed.
Keynes argued that because there was no guarantee that the goods that individuals produce would be met with demand, periodic unemployment could be expected from time to time, especially in the instance of an economy undergoing contraction.
He saw the economy as unable to maintain itself at full employment automatically, and believed that it was necessary for the government to step in and put purchasing power into the hands of the working population through government spending. Thus, according to Keynesian theory, some individually rational microeconomic-level actions such as not investing savings in the goods and services produced by the economy, if taken collectively by a large proportion of individuals and firms, can lead to outcomes wherein the economy operates below its potential output and growth rate.
Prior to Keynes, a situation in which aggregate demand for goods and services did not meet supply was referred to by classical economists as a general glut, although there was disagreement among them as to whether a general glut was possible. Keynes argued that when a glut occurred, it was the over-reaction of producers and the laying off of workers that led to a fall in demand and perpetuated the problem. Keynesians therefore advocate an active stabilization policy to reduce the amplitude of the business cycle, which they rank among the most serious of economic problems. According to the theory, government spending can be used to increase aggregate demand, thus increasing economic activity, reducing unemployment and deflation.
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Keynes argued that the solution to the Great Depression was to stimulate the country ("inducement to invest") through some combination of two approaches:
If the interest rate at which businesses and consumers can borrow is decreased, investments which were previously uneconomic become profitable, and large consumer sales which are normally financed through debt (such as houses, automobiles, and, historically, even appliances like refrigerators) become more affordable. A principal function of central banks in countries which have them is to influence this interest rate through a variety of mechanisms which are collectively called monetary policy. This is how monetary policy which reduces interest rates is thought to stimulate economic activity, i.e. "grow the economy", and why it is called expansionary monetary policy.
Expansionary fiscal policy consists of increasing net public spending, which the government can effect by a) taxing less, b) spending more, or c) both. Investment and consumption by government raises demand for businesses' products and for employment, reversing the effects of the aforementioned imbalance. If desired spending exceeds revenue, the government finances the difference by borrowing from capital markets by issuing government bonds. This is called deficit spending. Two points are important to note at this point. First, deficits are not required for expansionary fiscal policy, and second, it is only change in net spending that can stimulate or depress the economy. For example, if a government ran a deficit of 10% both last year and this year, this would represent neutral fiscal policy. In fact, if it ran a deficit of 10% last year and 5% this year, this would actually be contractionary. On the other hand, if the government ran a surplus of 10% of GDP last year and 5% this year, that would be expansionary fiscal policy, despite never running a deficit at all.
In the price mechanism of neoclassical economics, it is predicted that, in a competitive market, if demand for a particular good or service falls, that would immediately cause the price for that good or service to fall, which in turn would decrease supply and increase demand, thereby bringing them back to equilibrium. A central conclusion of Keynesian economics, in strong contrast to the previously dominant models of neoclassical synthesis, is that there are some situations in which a depressed economy would not quickly self-correct towards full employment and potential output, but could remain trapped indefinitely with both high unemployment and mothballed factories. To the observation that these were, in fact, the prevailing conditions throughout the industrialized world for many years during the Great Depression, classical models could only conclude that it was a temporary aberration. The purpose of Keynes' theory was to show such conditions could, without intervention, persist in a stable, though dismal, equilibrium.
By the end of the Second World War, Keynesianism was the most popular school of economic theory in the non-Communist world. Beginning in the late 1960s, a new classical macroeconomics movement arose, critical of Keynesian assumptions (see sticky prices), and seemed, especially in the 1970s, to explain certain phenomena (e.g. the co-existence of high unemployment and high inflation, or "stagflation") better. It was characterized by explicit and rigorous adherence to microfoundations, as well as use of increasingly sophisticated mathematical modelling. However, by the late 1980s, certain failures of the new classical models, both theoretical (see Real business cycle theory) and empirical (see the "Volcker recession") hastened the emergence of New Keynesian economics, a school which sought to unite the most realistic aspects of Keynesian and neo-classical assumptions and place them on more rigorous theoretical foundation than ever before.
Interpretations of Keynes have emphasized his stress on the international coordination of Keynesian policies, the need for international economic institutions, and the ways in which economic forces could lead to war or could promote peace.
Keynes's economic ideas are set forward in his main work, The General Theory of Employment, Interest and Money (1936), comprising more than 400 pages. Ever since it was published there has been debate over its meaning. A longer and more systematic summary of its contents (including reference to divergent interpretations) is given in the article on the General Theory.
Keynes begins the General theory with a summary of the classical theory of employment as he saw it, which he encapsulates in his formulation of Say's Law as the dictum 'Supply creates its own demand'.
Under the classical theory the wage rate is determined by the marginal productivity of labour, and as many people will be employed as are willing to take work at that rate. Unemployment may arise through friction or may be 'voluntary' in the sense that it arises from a refusal to accept employment owing to 'legislation or social practices... or mere human obstinacy', but 'the classical postulates do not admit of the possibility of the third category' which Keynes defines as 'involuntary unemployment'.
Keynes raises two objections to the classical theory's assumption that 'wage bargains... determine the real wage'. The first lies in the fact that 'labour stipulates (within limits) for a money-wage rather than a real wage'. The second is that classical theory assumes that 'the real wages of labour depend on the wage bargains which labour makes with the entrepreneurs' whereas 'if money wages change, one would have expected the classical school to argue that prices would change in almost the same proportion, leaving the real wage and the level of unemployment practically the same as before'. Keynes considers the second objection to be the more fundamental, but his expectation concerning the classical school contradicts the Quantity theory of money and most commentators have concentrated on his first objection.
Having rejected the classical theory that unemployment is due to excessive wages, Keynes proposes his alternative which is based on the relationship between saving and investment. In his view unemployment arises whenever entrepreneurs' inducement to invest fails to keep pace with society's propensity to save. The levels of saving and investment are necessarily equal, and income is therefore held down to a level at which the desire to save is no greater than the inducement to invest.
The inducement to invest arises from the interplay between the physical circumstances of production and psychological anticipations of future profitability; but once these things are given the inducement is independent of income and depends solely on the rate of interest r. Keynes designates its value as a function of r as the 'schedule of the marginal efficiency of capital'.
The propensity to save behaves quite differently. Saving is simply that part of income which is not devoted to consumption, and:
...the prevailing psychological law seems to be that when aggregate income increases, consumption expenditure will also increase but to a somewhat lesser extent.
Keynes adds that "this psychological law was of the utmost importance in the development of my own thought". If consumption increases to a somewhat lesser extent than aggregate income, then saving must increase to a somewhat greater extent.
Keynes viewed the money supply as one of the main determinants of the state of the real economy. The significance he attributed to it is one of the innovative features of his work, and was influential on the politically hostile monetarist school.
Money supply comes into play through the 'liquidity preference' function which specifies the amount of money people will choose to hold according to the state of the economy. In Keynes's first (and simplest) account liquidity preference is a function solely of the interest rate r which is seen as the earnings forgone by holding wealth in liquid form: hence liquidity preference can be written L(r ) and in equilibrium must equal the externally fixed money supply M?.
Money supply, saving and investment combine to determine the level of income as illustrated in the diagram, where the top graph shows money supply (on the vertical axis) against interest rate. M? determines the ruling interest rate r? through the liquidity preference function. The rate of interest determines the level of investment Î through the schedule of the marginal efficiency of capital, shown as a blue curve in the lower graph. The red curves in the same diagram show what the propensities to save will be for different incomes Y ; and the income ? corresponding to the equilibrium state of the economy must be the one for which the implied level of saving at the established interest rate is equal to Î.
In Keynes's more complicated liquidity preference theory, the demand for money depends on income as well as on the interest rate and the analysis becomes more complicated. Keynes never fully integrated his second liquidity preference doctrine with the rest of his theory, leaving the task to be completed by John Hicks: see the IS-LM model below.
Although Keynes rejects the classical explanation of unemployment based on excessive wages it is not clear what effect the wage rate has on unemployment in his own system. He treats the wages of all workers as proportional to a single rate set by collective bargaining, and chooses his units so that this rate never appears separately in his discussion. It is present implicitly in those quantities which are expressed in wage units while being absent from those expressed in money terms. It is therefore extremely difficult to see whether, and in what way, his results would differ for a different wage rate; nor is it entirely clear what he thought on the matter.
An increase in the money supply, according to Keynes's theory, will lead to a drop in the interest rate and to an increase in the amount of investment which can be profitably undertaken, bringing with it an increase in total income.
Keynes's name is associated with fiscal rather than monetary measures but they receive only passing (and often satirical) reference in the General Theory. He mentions 'increased public works' as an example of something which brings employment through the 'multiplier', but this is before he has developed the relevant theory, and the idea isn't followed up when the theory becomes available.
Later in the same chapter he tells us that:
Ancient Egypt was doubly fortunate, and doubtless owed to this its fabled wealth, in that it possessed two activities, namely, pyramid-building as well as the search for the precious metals, the fruits of which, since they could not serve the needs of man by being consumed, did not stale with abundance. The Middle Ages built cathedrals and sang dirges. Two pyramids, two masses for the dead, are twice as good as one; but not so two railways from London to York.
But again the implied recommendation to engage in public works, even if they are not fully justified from their direct benefits, is not taken up when the theory has been constructed. On the contrary he advises us later that...
...our final task might be to select those variables which can be deliberately controlled or managed by central authority in the kind of system in which we actually live...
and this appears to look forward to a future publication rather than to a subsequent chapter of the General Theory.
Keynes's view of saving and investment was his most important departure from the classical outlook. It can be illustrated using the 'Keynesian cross' devised by Paul Samuelson. The horizontal axis denotes total income and the purple curve shows C (Y ), the propensity to consume, whose complement S (Y ) is the propensity to save: the sum of these two functions is equal to total income which is shown by the broken line at 45°.
The horizontal blue line Is (r ) is the schedule of the marginal efficiency of capital whose value is independent of Y. Keynes interprets this as the demand for investment and denotes the sum of demands for consumption and investment as 'aggregate demand', plotted as a separate curve. Aggregate demand must equal total income, so equilibrium income must be determined by the point at which the aggregate demand curve crosses the 45° line. This is the same horizontal position as the intersection of Is (r ) with S (Y ).
This discussion illustrates the main points of difference between Keynes and his predecessors. The classics - in a tradition dating back to Turgot - had recognized the significance of Is (r ) but had identified it as the supply function for investment. This explains, for instance, how it is capable of being greater than total income. For them it would have made no sense to add the supply function Is (r ) to the demand function C (Y ).
At the same time the classics had considered S (Y ) to be the true demand for investment, since saving and investment were for them the same thing (albeit indirect in the latter case). Keynes takes note of this view in Chapter 2, where he finds it present in the early writings of Alfred Marshall but adds that 'the doctrine is never stated to-day in this crude form'.
The classics accepted the equation Is (r ) = S (Y ), viewing it as the condition of equilibrium between supply and demand for investment funds and as determining the interest rate (see the classical theory of interest). Interestingly Paul Krugman accepts the identification of Is (r ) as a supply function in his essay 'Mr Keynes and the moderns' while having identified it as 'a component of desired spending' and added it to the propensity to consume a few paragraphs earlier.
The equation Is (r ) = S (Y ) is accepted by Keynes for either or both of the following reasons:
These arguments support each other under Keynes's assumptions but might contradict each other under more general ones, e.g. if one sought to allow for foreign trade as in the Mundell-Fleming model.
Richard Kahn had written a 1931 paper claiming that a snowball of expenditure caused an avalanche of extra employment through the same money being spent repeatedly by its successive recipients. Keynes references his paper in Chapter 10 of the General Theory and declares his acceptance of Kahn's theory. This avowal has been taken at face value in much of the Keynesian secondary literature. Kahn's multiplier receives a clear statement in Samuelson's Economics and gives the title ('The multiplier model') to his account of Keynesian theory. It receives a similarly prominent position in Alvin Hansen's Guide to Keynes and in Joan Robinson's Introduction to the theory of employment.
It therefore comes as a surprise to find that Kahn's multiplier plays no role in the General Theory ; but Keynes's account of his own multiplier is so badly written that it is inevitable that people would seek enlightenment elsewhere.
Keynes's own multiplier is simply a measure of the response of one variable in his economic system to a change in another. It tells us 'the ratio... between an increment of investment and the corresponding increment of aggregate income'.G. L. S. Shackle regarded Keynes's departure from Kahn's multiplier as...
...a retrograde step... For when we look upon the Multiplier as an instantaneous functional relation... we are merely using the word Multiplier to stand for an alternative way of looking at the marginal propensity to consume...
which G. M. Ambrosi cites as an instance of "a Keynesian commentator who would have liked Keynes to have written something less 'retrograde' ".
Hansen made an unconvincing attempt to reconcile Keynes's multiplier with Kahn's: see The General Theory of Employment, Interest and Money.
There is no unique formula for the multiplier: it depends on the details of the economic system supporting it, and this is not fully defined since at different times Keynes adopts different views of liquidity preference. Under his earlier doctrine the rate of interest is unchanged by a change in investment and the effect is borne fully by income, leading to a multiplier equal to the reciprocal of the marginal propensity to save: k = 1 / S '(Y ). Under his later doctrine the effect is disributed between interest rate and income in proportions depending on the partial derivatives of the liquidity preference function. The resulting multiplier has a more complicated formula and a smaller numerical value.
The liquidity trap is a phenomenon which may impede the effectiveness of monetary policies in reducing unemployment.
It has generally been considered that the rate of interest would not fall below a certain limit, often seen as zero or a slightly negative number. Keynes suggested that the limit might be appreciably greater than zero but did not attach much practical significance to it. The term 'liquidity trap' was coined by Dennis Robertson in his comments on the General Theory , but it was John Hicks in "Mr. Keynes and the classics"  who recognised the significance of a slightly different concept.
If the economy is in a position such that the liquidity preference curve is almost vertical, as must happen as the lower limit on r is approached, then a change in the money supply M? will make almost no difference to the equilibrium rate of interest r? or, unless there is compensating steepness in the other curves, to the resulting income ?. As Hicks put it, 'monetary means will not force down the rate of interest any further'.
Paul Krugman has worked extensively on the liquidity trap, claiming that it was the problem confronting the Japanese economy around the turn of the millennium. In his later words:
Short-term interest rates were close to zero, long-term rates were at historical lows, yet private investment spending remained insufficient to bring the economy out of deflation. In that environment, monetary policy was just as ineffective as Keynes described. Attempts by the Bank of Japan to increase the money supply simply added to already ample bank reserves and public holdings of cash...
Hicks showed how to analyze Keynes's system when liquidity preference is a function of income as well as of the rate of interest. Keynes's admission of income as an influence on the demand for money is a step back in the direction of classical theory, and Hicks takes a further step in the same direction by generalizing the propensity to save to take both Y and r as arguments. Less classically he extends this generalization to the schedule of the marginal efficiency of capital.
Keynes's model is expressed by two equations. The first, now written Is (Y,r ) = S (Y,r ), expresses the principle of effective demand. We may construct a graph on (Y,r ) coordinates and draw a line connecting those points satisfying the equation: this is the IS curve. In the same way we can write the equation of equilibrium between liquidity preference and the money supply as L(W ·Y ,r ) = M? and draw a second curve - the LM curve - connecting points which satisfy it. (The 'W ' here is the wage rate, and is needed because income needs to be converted from Keynes's wage units to money units in order for the equation to make sense.)
The equilibrium values ? of total income and r? of interest rate are then given by the point of intersection of the two curves.
If we follow Keynes's initial account under which liquidity preference depends only on the interest rate r, then the LM curve will be horizontal.
Joan Robinson commented that:
...modern teaching has been confused by J. R. Hicks' attempt to reduce the General Theory to a version of static equilibrium with the formula IS/LM. Hicks has now repented and changed his name from J. R. to John, but it will take a long time for the effects of his teaching to wear off.
Hicks subsequently relapsed.
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Classical economists have traditionally advocated balanced government budgets. Keynesians, on the other hand, believe that it is entirely legitimate and appropriate for governments to incur expenditure in excess of taxation revenues during periods of economic stagnation such as the Great Depression, which dominated economic life at the time he was developing and publicizing his theories.
Contrary to some critical characterizations of it, Keynesianism does not consist solely of deficit spending. Keynesianism recommends counter-cyclical policies. An example of a counter-cyclical policy is raising taxes to cool the economy and to prevent inflation when there is abundant demand-side growth, and engaging in deficit spending on labour-intensive infrastructure projects to stimulate employment and stabilize wages during economic downturns. Classical economics, on the other hand, argues that one should cut taxes when there are budget surpluses, and cut spending - or, less likely, increase taxes - during economic downturns.
Keynes's ideas influenced Franklin D. Roosevelt's view that insufficient buying-power caused the Depression. During his presidency, Roosevelt adopted some aspects of Keynesian economics, especially after 1937, when, in the depths of the Depression, the United States suffered from recession yet again following fiscal contraction. But to many the true success of Keynesian policy can be seen at the onset of World War II, which provided a kick to the world economy, removed uncertainty, and forced the rebuilding of destroyed capital. Keynesian ideas became almost official in social-democratic Europe after the war and in the U.S. in the 1960s.
Keynes developed a theory which suggested that active government policy could be effective in managing the economy. Rather than seeing unbalanced government budgets as wrong, Keynes advocated what has been called countercyclical fiscal policies, that is, policies that acted against the tide of the business cycle: deficit spending when a nation's economy suffers from recession or when recovery is long-delayed and unemployment is persistently high - and the suppression of inflation in boom times by either increasing taxes or cutting back on government outlays. He argued that governments should solve problems in the short run rather than waiting for market forces to do it in the long run, because, "in the long run, we are all dead."
This contrasted with the classical and neoclassical economic analysis of fiscal policy. Fiscal stimulus could actuate production. But, to these schools, there was no reason to believe that this stimulation would outrun the side-effects that "crowd out" private investment: first, it would increase the demand for labour and raise wages, hurting profitability; Second, a government deficit increases the stock of government bonds, reducing their market price and encouraging high interest rates, making it more expensive for business to finance fixed investment. Thus, efforts to stimulate the economy would be self-defeating.
The Keynesian response is that such fiscal policy is appropriate only when unemployment is persistently high, above the non-accelerating inflation rate of unemployment (NAIRU). In that case, crowding out is minimal. Further, private investment can be "crowded in": Fiscal stimulus raises the market for business output, raising cash flow and profitability, spurring business optimism. To Keynes, this accelerator effect meant that government and business could be complements rather than substitutes in this situation.
Second, as the stimulus occurs, gross domestic product rises, raising the amount of saving, helping to finance the increase in fixed investment. Finally, government outlays need not always be wasteful: government investment in public goods that will not be provided by profit-seekers will encourage the private sector's growth. That is, government spending on such things as basic research, public health, education, and infrastructure could help the long-term growth of potential output.
Keynesian economists believe that adding to profits and incomes during boom cycles through tax cuts, and removing income and profits from the economy through cuts in spending during downturns, tends to exacerbate the negative effects of the business cycle. This effect is especially pronounced when the government controls a large fraction of the economy, as increased tax revenue may aid investment in state enterprises in downturns, and decreased state revenue and investment harm those enterprises.
In the last few years of his life, John Maynard Keynes was much preoccupied with the question of balance in international trade. He was the leader of the British delegation to the United Nations Monetary and Financial Conference in 1944 that established the Bretton Woods system of international currency management. He was the principal author of a proposal - the so-called Keynes Plan - for an International Clearing Union. The two governing principles of the plan were that the problem of settling outstanding balances should be solved by 'creating' additional 'international money', and that debtor and creditor should be treated almost alike as disturbers of equilibrium. In the event, though, the plans were rejected, in part because "American opinion was naturally reluctant to accept the principle of equality of treatment so novel in debtor-creditor relationships".
The new system is not founded on free-trade (liberalisation of foreign trade) but rather on the regulation of international trade, in order to eliminate trade imbalances: the nations with a surplus would have a powerful incentive to get rid of it, and in doing so they would automatically clear other nations deficits. He proposed a global bank that would issue its own currency - the bancor - which was exchangeable with national currencies at fixed rates of exchange and would become the unit of account between nations, which means it would be used to measure a country's trade deficit or trade surplus. Every country would have an overdraft facility in its bancor account at the International Clearing Union. He pointed out that surpluses lead to weak global aggregate demand - countries running surpluses exert a "negative externality" on trading partners, and posed far more than those in deficit, a threat to global prosperity. In "National Self-Sufficiency" The Yale Review, Vol. 22, no. 4 (June 1933) , he already highlighted the problems created by free trade.
His view, supported by many economists and commentators at the time, was that creditor nations may be just as responsible as debtor nations for disequilibrium in exchanges and that both should be under an obligation to bring trade back into a state of balance. Failure for them to do so could have serious consequences. In the words of Geoffrey Crowther, then editor of The Economist, "If the economic relationships between nations are not, by one means or another, brought fairly close to balance, then there is no set of financial arrangements that can rescue the world from the impoverishing results of chaos."
These ideas were informed by events prior to the Great Depression when - in the opinion of Keynes and others - international lending, primarily by the U.S., exceeded the capacity of sound investment and so got diverted into non-productive and speculative uses, which in turn invited default and a sudden stop to the process of lending.
Influenced by Keynes, economic texts in the immediate post-war period put a significant emphasis on balance in trade. For example, the second edition of the popular introductory textbook, An Outline of Money, devoted the last three of its ten chapters to questions of foreign exchange management and in particular the 'problem of balance'. However, in more recent years, since the end of the Bretton Woods system in 1971, with the increasing influence of Monetarist schools of thought in the 1980s, and particularly in the face of large sustained trade imbalances, these concerns - and particularly concerns about the destabilising effects of large trade surpluses - have largely disappeared from mainstream economics discourse and Keynes' insights have slipped from view. They are receiving some attention again in the wake of the financial crisis of 2007-08.
Keynes's work was part of a long-running debate within economics over the existence and nature of general gluts. While a number of the policies Keynes advocated (the notable one being government deficit spending at times of low private investment or consumption) and the theoretical ideas he proposed (effective demand, the multiplier, the paradox of thrift) were advanced by various authors in the 19th and early 20th centuries, Keynes's unique contribution was to provide a general theory of these, which proved acceptable to the political and economic establishments.
An intellectual precursor of Keynesian economics was underconsumption theories associated with John Law, Thomas Malthus, the Birmingham School of Thomas Attwood, and the American economists William Trufant Foster and Waddill Catchings, who were influential in the 1920s and 1930s. Underconsumptionists were, like Keynes after them, concerned with failure of aggregate demand to attain potential output, calling this "underconsumption" (focusing on the demand side), rather than "overproduction" (which would focus on the supply side), and advocating economic interventionism. Keynes specifically discussed underconsumption (which he wrote "under-consumption") in the General Theory, in Chapter 22, Section IV and Chapter 23, Section VII.
Numerous concepts were developed earlier and independently of Keynes by the Stockholm school during the 1930s; these accomplishments were described in a 1937 article, published in response to the 1936 General Theory, sharing the Swedish discoveries.
The multiplier dates to work in the 1890s by the Australian economist Alfred de Lissa, the Danish economist Julius Wulff, and the German-American economist Nicholas Johannsen, the latter being cited in a footnote of Keynes. Nicholas Johannsen also proposed a theory of effective demand in the 1890s.
The paradox of thrift was stated in 1892 by John M. Robertson in his The Fallacy of Saving, in earlier forms by mercantilist economists since the 16th century, and similar sentiments date to antiquity.
Today these ideas, regardless of provenance, are referred to in academia under the rubric of "Keynesian economics", due to Keynes's role in consolidating, elaborating, and popularizing them.
Keynes's ideas became widely accepted after World War II, and until the early 1970s, Keynesian economics provided the main inspiration for economic policy makers in Western industrialized countries. Governments prepared high quality economic statistics on an ongoing basis and tried to base their policies on the Keynesian theory that had become the norm. In the early era of social liberalism and social democracy, most western capitalist countries enjoyed low, stable unemployment and modest inflation, an era called the Golden Age of Capitalism.
In terms of policy, the twin tools of post-war Keynesian economics were fiscal policy and monetary policy. While these are credited to Keynes, others, such as economic historian David Colander, argue that they are, rather, due to the interpretation of Keynes by Abba Lerner in his theory of functional finance, and should instead be called "Lernerian" rather than "Keynesian".
Through the 1950s, moderate degrees of government demand leading industrial development, and use of fiscal and monetary counter-cyclical policies continued, and reached a peak in the "go go" 1960s, where it seemed to many Keynesians that prosperity was now permanent. In 1971, Republican US President Richard Nixon even proclaimed "I am now a Keynesian in economics."
However, with the oil shock of 1973, and the economic problems of the 1970s, Keynesian economics began to fall out of favour. During this time, many economies experienced high and rising unemployment, coupled with high and rising inflation, contradicting the Phillips curve's prediction. This stagflation meant that the simultaneous application of expansionary (anti-recession) and contractionary (anti-inflation) policies appeared to be necessary. This dilemma led to the end of the Keynesian near-consensus of the 1960s, and the rise throughout the 1970s of ideas based upon more classical analysis, including monetarism, supply-side economics, and new classical economics.
At the same time, Keynesians began during the period to reorganize their thinking (some becoming associated with New Keynesian economics). One strategy, utilized also as a critique of the notably high unemployment and potentially disappointing GNP growth rates associated with the latter two theories by the mid-1980s, was to emphasize low unemployment and maximal economic growth at the cost of somewhat higher inflation (its consequences kept in check by indexing and other methods, and its overall rate kept lower and steadier by such potential policies as Martin Weitzman's share economy).
Multiple schools of economic thought that trace their legacy to Keynes currently exist, the notable ones being Neo-Keynesian economics, New Keynesian economics, and Post-Keynesian economics. Keynes's biographer Robert Skidelsky writes that the post-Keynesian school has remained closest to the spirit of Keynes's work in following his monetary theory and rejecting the neutrality of money.
In the postwar era, Keynesian analysis was combined with neoclassical economics to produce what is generally termed the "neoclassical synthesis", yielding Neo-Keynesian economics, which dominated mainstream macroeconomic thought. Though it was widely held that there was no strong automatic tendency to full employment, many believed that if government policy were used to ensure it, the economy would behave as neoclassical theory predicted. This post-war domination by Neo-Keynesian economics was broken during the stagflation of the 1970s. There was a lack of consensus among macroeconomists in the 1980s. However, the advent of New Keynesian economics in the 1990s, modified and provided microeconomic foundations for the neo-Keynesian theories. These modified models now dominate mainstream economics.
Post-Keynesian economists, on the other hand, reject the neoclassical synthesis and, in general, neoclassical economics applied to the macroeconomy. Post-Keynesian economics is a heterodox school that holds that both Neo-Keynesian economics and New Keynesian economics are incorrect, and a misinterpretation of Keynes's ideas. The Post-Keynesian school encompasses a variety of perspectives, but has been far less influential than the other more mainstream Keynesian schools.
The Keynesian schools of economics are situated alongside a number of other schools that have the same perspectives on what the economic issues are, but differ on what causes them and how to best resolve them:
The Stockholm school rose to prominence at about the same time that Keynes published his General Theory and shared a common concern in business cycles and unemployment. The second generation of Swedish economists also advocated government intervention through spending during economic downturns although opinions are divided over whether they conceived the essence of Keynes's theory before he did.
There was debate between Monetarists and Keynesians in the 1960s over the role of government in stabilizing the economy. Both Monetarists and Keynesians agree that issues such as business cycles, unemployment, and deflation are caused by inadequate demand. However, they had fundamentally different perspectives on the capacity of the economy to find its own equilibrium, and the degree of government intervention that would be appropriate. Keynesians emphasized the use of discretionary fiscal policy and monetary policy, while monetarists argued the primacy of monetary policy, and that it should be rules-based.
The debate was largely resolved in the 1980s. Since then, economists have largely agreed that central banks should bear the primary responsibility for stabilizing the economy, and that monetary policy should largely follow the Taylor rule - which many economists credit with the Great Moderation. The financial crisis of 2007-08, however, has convinced many economists and governments of the need for fiscal interventions and highlighted the difficulty in stimulating economies through monetary policy alone during a liquidity trap.
Some Marxist economists criticized Keynesian economics. For example, in his 1946 appraisalPaul Sweezy, while admitting that there was much in the General Theory's analysis of effective demand which Marxists could draw upon, described Keynes as in the last resort a prisoner of his neoclassical upbringing. Sweezy argued Keynes had never been able to view the capitalist system as a totality. He argued Keynes had regarded the class struggle carelessly, and overlooked the class role of the capitalist state, which he treated as a deus ex machina, and some other points. While Micha? Kalecki was generally enthusiastic about the Keynesian revolution, he predicted that it would not endure, in his article "Political Aspects of Full Employment". In the article Kalecki predicted that the full employment delivered by Keynesian policy would eventually lead to a more assertive working class and weakening of the social position of business leaders, causing the elite to use their political power to force the displacement of the Keynesian policy even though profits would be higher than under a laissez faire system: The erosion of social prestige and political power would be unacceptable to the elites despite higher profits.
James M. Buchanan criticized Keynesian economics on the grounds that governments would in practice be unlikely to implement theoretically optimal policies. The implicit assumption underlying the Keynesian fiscal revolution, according to Buchanan, was that economic policy would be made by wise men, acting without regard to political pressures or opportunities, and guided by disinterested economic technocrats. He argued that this was an unrealistic assumption about political, bureaucratic and electoral behaviour. Buchanan blamed Keynesian economics for what he considered a decline in America's fiscal discipline. Buchanan argued that deficit spending would evolve into a permanent disconnect between spending and revenue, precisely because it brings short-term gains, so, ending up institutionalizing irresponsibility in the federal government, the largest and most central institution in our society.Martin Feldstein argues that the legacy of Keynesian economics-the misdiagnosis of unemployment, the fear of saving, and the unjustified government intervention-affected the fundamental ideas of policy makers.Milton Friedman thought that Keynes's political bequest was harmful for two reasons. First, he thought whatever the economic analysis, benevolent dictatorship is likely sooner or later to lead to a totalitarian society. Second, he thought Keynes's economic theories appealed to a group far broader than economists primarily because of their link to his political approach.Alex Tabarrok argues that Keynesian politics-as distinct from Keynesian policies-has failed pretty much whenever it's been tried, at least in liberal democracies.
In response to this argument, John Quiggin, wrote about these theories' implication for a liberal democratic order. He thought if it is generally accepted that democratic politics is nothing more than a battleground for competing interest groups, then reality will come to resemble the model. Paul Krugman wrote "I don't think we need to take that as an immutable fact of life; but still, what are the alternatives?"  Daniel Kuehn, criticized James M. Buchanan. He argued, "if you have a problem with politicians - criticize politicians," not Keynes. He also argued that empirical evidence makes it pretty clear that Buchanan was wrong.James Tobin argued, if advising government officials, politicians, voters, it's not for economists to play games with them. Keynes implicitly rejected this argument, in "soon or late it is ideas not vested interests which are dangerous for good or evil."
Brad DeLong has argued that politics is the main motivator behind objections to the view that government should try to serve a stabilizing macroeconomic role.Paul Krugman argued that a regime that by and large lets markets work, but in which the government is ready both to rein in excesses and fight slumps is inherently unstable, due to intellectual instability, political instability, and financial instability.
Another influential school of thought was based on the Lucas critique of Keynesian economics. This called for greater consistency with microeconomic theory and rationality, and in particular emphasized the idea of rational expectations. Lucas and others argued that Keynesian economics required remarkably foolish and short-sighted behaviour from people, which totally contradicted the economic understanding of their behaviour at a micro level. New classical economics introduced a set of macroeconomic theories that were based on optimizing microeconomic behaviour. These models have been developed into the real business-cycle theory, which argues that business cycle fluctuations can to a large extent be accounted for by real (in contrast to nominal) shocks.
Beginning in the late 1950s new classical macroeconomists began to disagree with the methodology employed by Keynes and his successors. Keynesians emphasized the dependence of consumption on disposable income and, also, of investment on current profits and current cash flow. In addition, Keynesians posited a Phillips curve that tied nominal wage inflation to unemployment rate. To support these theories, Keynesians typically traced the logical foundations of their model (using introspection) and supported their assumptions with statistical evidence. New classical theorists demanded that macroeconomics be grounded on the same foundations as microeconomic theory, profit-maximizing firms and rational, utility-maximizing consumers.
The result of this shift in methodology produced several important divergences from Keynesian macroeconomics: