Private consumption expenditure accounts for about two-thirds of gross domestic product (GDP) in most developed countries, with the remaining one-third accounted for by business and government expenditures and net exports. A substantial portion of government expenditure (e.g., spending on public health programs) is also considered to be consumption expenditure, as it provides a service that consumers value.

In national income accounting, private consumption expenditure is divided into three broad categories: expenditures for services, for durable goods, and for nondurable goods. Durable goods are generally defined as those whose expected lifetime is greater than three years, and spending on durable goods is much more volatile than spending in the other two categories. Services include a broad range of items including telephone and utility service, legal and financial services, and travel and lodging services. Nondurable goods include food and other immediately perishable items (sometimes called “strictly nondurable goods”) as well as some items that can be expected to last for a substantial period of time, such as clothing.

The distinction between the flow of consumption as economists conceive it (including the services of durable goods owned by households) and consumption expenditure as measured in national income accounts is vital to understanding macroeconomic fluctuations. Producers (and therefore employers) make money only from the sale of a durable good, not from its continuing use after the sale. Therefore, it is the level of consumption expenditure—not the flow of consumption as defined above—that determines short-term macroeconomic prosperity (or otherwise).

Macroeconomists have accordingly extended the rational optimization framework to account for the “lumpy” nature of durable goods (i.e., a large purchase is made in a single moment, but its usefulness extends over a long period; one cannot buy 1 20 of a new automobile). Both theory and evidence suggest roughly the following story. In an economic downturn, expenditures on durable goods such as automobiles generally plummet because many consumers who had been considering replacement of their durable goods decide to hold off either until the economy improves or until their need to replace the durable good becomes sufficiently urgent. The early phase of economic recoveries generally exhibits a surge in spending on durable goods as this process is reversed. More broadly, spending on durable goods tends to be much more volatile than spending on nondurables and services, because all that is needed to induce a surge in durables spending is something that pushes consumers from merely contemplating a purchase to actually making a purchase. This logic explains why spending on durables is much more sensitive to interest rates, rebates, and other economic stimuli than are other kinds of spending.

The impetus for the modern consumption literature comes largely from John Maynard Keynes, The General Theory of Employment, Interest, and Money (1936); although Keynes’s model of the consumption function has been superseded, there is still much wisdom in his discussion. The two classic references that form the foundation of the modern life-cycle and permanent-income theories of consumption are Franco Modigliani and Richard Brumberg, “Utility Analysis and the Consumption Function: An Interpretation of Cross-Section Data,” in Kenneth K. Kurihara (ed.), Post-Keynesian Economics (1954, reissued 1993), pp. 388–436; and Milton Friedman, A Theory of the Consumption Function (1957). An excellent summary of the literature can be found in Angus Deaton, Understanding Consumption (1992). An overview of the current baseline model and of the relationship between the mathematically rigorous versions of the life-cycle and permanent-income-hypothesis models is given in Christopher D. Carroll (1997), “Buffer-Stock Saving and the Life Cycle/Permanent Income Hypothesis,” The Quarterly Journal of Economics, 107(1):1–56 (1997).

Perspectives that deviate from the current baseline framework have a venerable history, starting with Adam Smith, An Inquiry into the Nature and Causes of the Wealth of Nations (1776); of particular interest is chapter 2, where Smith argues that people care about how their consumption compares to that of others. Thorstein Veblen, The Theory of the Leisure Class (1899, reissued 1998), provides an extended treatment of this idea and introduces the phrase “conspicuous consumption.” Many related issues are discussed in Robert H. Frank, Choosing the Right Pond (1985). The introduction of Christopher D. Carroll, Jody Overland, and David N. Weil, “Saving and Growth with Habit Formation,” American Economic Review, 90(3):341–355 (2000), gives a summary of the evidence that habit formation may play an important role in explaining a wide variety of puzzles in macroeconomics. The seminal paper in the modern literature on self-control problems in consumption is David Laibson, “Golden Eggs and Hyperbolic Discounting,” The Quarterly Journal of Economics, 112(2):443–477 (1997).