Many explanations of the reasons for economic fluctuation have been advanced throughout history. Even the most rudimentary explanation of cycles must isolate the forces and relationships that tend to produce these recurrent movements. The more comprehensive theories must in addition explain why, during downturns, (1) employment falls and unemployment increases and (2) investment declines by a much greater percent than output.

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William Stanley Jevons, engraving.

BBC Hulton Picture Library/Globe Photos

Perhaps the oldest theories of the business cycle are those that link their cause to fluctuations of the harvest. Since crops depend upon soil, climate, and other natural factors that in turn may be affected by biological or meteorological cycles, such cycles will transmit their effects through the harvests to the rest of the economy. The 19th-century British economist William Stanley Jevons thought he had found the key to such a process in the behaviour of sunspots, which seemed to display a 10-year cycle. His naïve explanation could not long withstand critical examination. It attracted a certain interest, however, for suggesting a causal factor that was completely detached from the economic system and one that could not be influenced by it in turn. Agricultural theories made sense in the 19th century and earlier, when agricultural products represented between 40 and 60 percent of the output of advanced economies. By the turn of the 21st century, however, agriculture’s contribution to the outputs of advanced economies had fallen to 5 percent or less.

A number of writers have explored mass psychology and its consequences for economic behaviour. Individuals are strongly influenced by the beliefs of the group or groups to which they belong. There are times when the general mood is optimistic and others when it is pessimistic. British economist Arthur C. Pigou, in his Industrial Fluctuations (1927), put forward a theory of what he called “noncompensated errors.” He pointed out that, if individuals behave in a completely autonomous way, their errors in expectations will tend to offset each other. But if they imitate each other, their errors will accumulate, eventually acquiring a global magnitude that may have powerful economic effects. This “follow-the-crowd” tendency is a factor in the ups and downs of the stock market, in financial booms and crashes, and in the behaviour of investors. One can say, however, that this psychological factor is not enough to explain economic fluctuations; rather, moods of optimism and pessimism themselves are probably rooted in economic factors.

Some observers have maintained that economic fluctuations result from political events. Even the imposition of a tax or an import restriction may have some dynamic effect upon the economy. In the United States, for example, some economists have speculated that incumbent political leaders pressure the chairman of the Federal Reserve System to loosen monetary policy in advance of an election as a means of fostering prosperity. It remains to be determined whether such political factors are capable of producing cyclical movements.

Ever since the start of the Industrial Revolution at the end of the 18th century, technical innovations have followed each other without end but not without pause. For example, cycles of rapid growth and measured accommodation took place after the introduction of the steam engine, the development of petroleum-based energy sources, the harnessing of electric power, and the invention of the computer and the creation of the Internet. It is possible that, if a rhythm could be found in these waves of change, the same rhythm might be responsible for corresponding movements in the economy. But it is equally possible that the technical innovations themselves have been dictated by the prior needs of the economy.

Even changes in population have been postulated as a cause of economic fluctuations. There are, undeniably, cyclical movements of population; it is possible to find fluctuations in the rates of marriage, birth, mortality, and migration, but the extent to which such fluctuations may be associated with changes in economic conditions is not clear.

In an expanding economy, production tends to grow more rapidly than consumption. The disparity results from the unequal distribution of income: the rich do not consume all their income, while the poor do not have sufficient income to meet their consumption needs. This imbalance between output and sales has led to theories that the business cycle is caused by overproduction or underconsumption. But the basic, underlying cause is society’s inadequate provision for an even flow of savings out of the excess of production over consumption. In other words, saving is out of step with the requirements of the economy; it is improperly distributed over time.

The fact that changes in the supply of savings, or loanable funds, are not closely coordinated with changes in the rest of the economy lies at the heart of the theories that link investment imbalance to the business cycle. Savings accumulate when there is no immediate outlet for them in the form of new investment opportunities. When times become more favourable, these savings are invested in new industrial projects, and a wave of investment occurs that sweeps the rest of the economy along with it. The new investment creates new income, which in turn acts as a further stimulus to investment. In 1894 an early observer of this phenomenon, the Russian economist Mikhayl Tugan-Baranovsky, published a study of industrial crises in England in which he maintained that the cycle of investment continues until all capital funds have been used up. Bank credit expands as the cycle progresses. Disproportions then begin to develop among the various branches of production as well as between production and consumption in general. These imbalances lead to a new period of stagnation and depression.