Consumption (economics)

• 1. Introduction

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  Consumption, in economic terms, is the act of using resources to fulfill present needs and desires. That simple definition hides an enormous range of disagreement. Economists have been debating what consumption actually means for nearly a century, and the answer shapes how governments measure national wealth, how households plan for retirement, and how individuals understand their own choices. Why do people spend money in ways they know hurt their long-term interests? Why does a windfall like winning a lottery not produce an immediate spending spree? And what happens to consumption habits when income falls, and people refuse to cut back? The answers run through the work of John Maynard Keynes, Milton Friedman, Franco Modigliani, and several other economists whose competing theories have defined how we understand modern economic life.

• 2. Defining the Term

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  Mainstream economists draw a tight boundary around what counts as consumption. Only the final purchase of newly produced goods and services by individuals for immediate use qualifies. Fixed investment, intermediate consumption, and government spending are placed in separate categories. Other economists take a far broader view. For them, consumption includes the entire aggregate of economic activity that does not involve designing, producing, or marketing goods: the selection, adoption, use, disposal, and recycling of things people buy. The Columbia School of Household Economics, also known as the New Home Economics, adds another layer by insisting that commercial consumption must be analyzed alongside household production. When someone cooks at home instead of ordering out, the opportunity cost of their time affects demand for commercial goods. Even who does the chores within a household, and how spouses compensate each other for that work, shapes the overall elasticity of demand for goods and services. Across countries, consumption typically accounts for between 45% and 85% of gross domestic product, making it the single largest component of GDP in most economies.

• 3. Keynes and the Income Hypothesis

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  John Maynard Keynes introduced the consumption function in his 1936 General Theory. His core claim was that in the short run, the most important determinant of consumer spending is real income. According to what became known as the Absolute Income Hypothesis, spending on goods and services is a linear function of a person's current disposable income. The formula captures two key ideas: autonomous consumption, the minimum spending a household maintains even by drawing down savings or borrowing; and the marginal propensity to consume, which reveals what fraction of additional income actually gets spent. Keynes was focused on current income and ignored future income entirely. James Duesenberry challenged this with his Relative Income Hypothesis in 1949. His model rested on two behavioral observations. First, people compare themselves to those around them: two individuals with the same income but different positions in the income distribution will spend differently, because what drives satisfaction is one's standing relative to others, a pattern Duesenberry called the Demonstration Effect. Second, consumer behavior over time is irreversible. When income falls, spending sticks to its previous level, because people resist cutting back once they have grown accustomed to a certain standard of living. Duesenberry called this the ratchet effect.

• 4. Friedman, Modigliani, and Lifetime Planning

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  Milton Friedman developed the Permanent Income Hypothesis in the 1950s, published in his book A Theory of the Consumption Function. Friedman divided income into two components: permanent income, the portion a person expects to receive over the long run, and transitory income, temporary windfalls or shortfalls. Only changes in permanent income produce proportional changes in consumption via the marginal propensity to consume. A transitory gain, like winning $1,000 with ten more years of life expected, would increase annual spending by only $100, spread across those remaining years. Franco Modigliani published the Life-Cycle Hypothesis in 1966. His model similarly treated consumption as a decision made across a whole lifetime. People draw on past accumulated wealth, expected future wages, and the number of working years they have left to smooth their spending from youth to old age. Both theories predict far more restrained responses to income shocks than Keynes had assumed, and both emerged partly as critiques of the limits of his absolute income framework. The model of intertemporal consumption that underlies both approaches traces back further, to John Rae in the 1830s, and was later expanded by Irving Fisher in the 1930s in his book Theory of Interest.

• 5. Behavioral Limits on Rationality

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  Behavioral economics challenges the assumption that people maximize utility within their budget constraints. Herbert Simon first proposed the concept of bounded rationality, the idea that people sometimes respond sensibly to their own cognitive limits by trying to minimize both the costs of making decisions and the costs of making errors. Bounded willpower is a separate phenomenon: people frequently take actions they know conflict with their long-term interests. Smokers who would prefer not to smoke and who are willing to pay for programs to help them quit illustrate this tension plainly. Bounded self-interest complicates the standard utility model further, because under certain circumstances many people behave as if they care about others, even strangers. In microeconomics, the standard model of consumer choice assumes people are rational and choose combinations of goods based on their utility function and their budget constraint. A special case is the consumption-leisure model, where a consumer allocates time between leisure and work, with the income from work representing the cost of leisure. Real shopping behavior, however, is also shaped by factors like the popularity of a product or its placement on a supermarket shelf, neither of which belong to the utility-maximizing framework.

• 6. What Drives Spending

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  Income is generally considered by economists to be the most influential factor affecting consumption levels. But several other variables interact with it. Consumer expectations about future prices can shift present spending decisions: if people anticipate price increases, they may buy now rather than later. Assets and wealth, including cash, bank deposits, securities, durable goods, and real estate, can supplement income in an emergency, but only if those assets are sufficiently liquid. Access to credit allows consumers to bring future income into the present, increasing current expenditure beyond what current income alone would permit. Interest rate changes also affect household decisions: higher rates make saving more attractive and tend to reduce current consumption. Household size matters too, with absolute consumption costs rising as families grow, though for some goods the increase is proportionate to fewer members than the total due to economies of scale. Social group also plays a role. Employers and workers show different consumption patterns, and the more unequal a society is, the more heterogeneous its overall consumption patterns tend to be. Geography adds another dimension: consumption patterns differ between urban and rural areas, between densely and sparsely populated regions, and between economically active and inactive areas.

• 7. Energy, Growth, and Access

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  Electrical energy consumption is positively correlated with economic growth, because energy is an essential input for producing goods and delivering services. Iran offers a documented example: electricity consumption there rose alongside economic growth from 1970 onward. As countries become more developed, however, the relationship tends to weaken, because more efficient equipment replaces older machinery and some production shifts to countries where energy is cheaper. A different kind of development in consumption thinking arrived with the concept of access-based consumption, the idea that people increasingly seek temporary access to goods rather than ownership of them. Social theorist Jeremy Rifkin put forward this idea in his 2000 publication The Age of Access. The sharing economy grew from this premise, though researchers Bardhi and Eckhardt have drawn careful distinctions between true sharing and mere access arrangements. A parallel shift is visible in retirement spending patterns. A 2017 study conducted in the United States found that 20% of married people considered leaving an inheritance a priority, while 34% did not. About 14% of unmarried Americans planned to spend their retirement funds on improving their own lives rather than preserving wealth for their children. The book Spending the Kids' Inheritance by Annie Hulley gave this trend a name, and the acronym SKI entered common use to describe it. A related concept, the Die Broke philosophy described in the book Die Broke: A Radical Four-Part Financial Plan by Stephen Pollan and Mark Levine, pushed the idea further: the goal is to spend down all assets over a lifetime rather than leave anything behind.