Markets, Prices, and Supply & Demand

What Is a Market?

In everyday speech, a market may mean a physical place where people buy and sell things. In economics, the term is broader.

A market is any arrangement through which buyers and sellers exchange goods, services, labor, or other things of value.

A market can be a farmers' market, a supermarket, a labor market, a housing market, an online marketplace, or a worldwide market for oil.

Markets do not require buyers and sellers to meet face to face. What matters is that potential buyers and sellers can compare alternatives and make exchanges.

Demand: The Buyer's Side

Demand describes how much of a good or service buyers are willing and able to purchase at different prices, other things being equal.

The words willing and able matter. Wanting a beachfront house does not create effective market demand if a person cannot afford one.

In general, when the price of something rises, people tend to buy less of it; when its price falls, they tend to buy more. Economists call this the law of demand.

There are several reasons this often happens:

• At a lower price, more buyers may be able to afford the product.
• Existing buyers may purchase more of it.
• Buyers may switch toward it from more expensive alternatives.

Demand is more than desire.

In ordinary conversation, we sometimes say there is “a lot of demand” for something simply because many people want it. Economics uses the term more precisely. Demand reflects both people's preferences and their ability to pay.

This distinction becomes especially important with necessities. Many households may strongly want better housing, medical care, or higher-quality food, but limited income can restrict how much they are able to purchase. A market responds to effective demand—what buyers are willing and able to buy—not simply to human need.

What else can change demand?

Demand can change even when the product's own price has not changed. Important influences include income, the prices of substitutes and related goods, changing preferences, population and demographic changes, and expectations about future prices or income.

For example, if beef becomes much more expensive, some shoppers may buy more chicken. If a community gains population, demand for housing may increase. If consumers expect car prices to rise soon, some may decide to buy earlier.

Supply: The Seller's Side

Supply describes how much of a good or service sellers are willing and able to offer at different prices, other things being equal.

In general, a higher price gives producers a greater incentive to supply a product. It may make additional production profitable or attract additional sellers into the market. A lower price can have the opposite effect.

Economists call this general relationship the law of supply.

Supply depends on costs and capacity.

A seller's decision is not based on price alone. Producers must also consider wages, raw materials, energy, rent, transportation, equipment, borrowing costs, taxes, and other expenses. If the selling price rises while costs stay the same, producing more may become worthwhile. If production costs rise too, the higher selling price may provide little additional incentive.

Technology can change supply as well. A production method that allows a business to produce more with the same labor and materials can make it profitable to offer more at a given price.

Time matters.

Some producers can respond quickly to higher prices; others cannot. A bakery may add another shift tomorrow. A manufacturer may need months to install equipment. A farmer may have to wait for the next planting season.

Housing is an especially important example. Rising rents may encourage construction, but acquiring land, arranging financing, receiving approvals, installing infrastructure, and completing buildings can take years. Supply may therefore remain limited even while prices are rising.

Supply and Demand Together

Buyers generally prefer lower prices. Sellers generally prefer higher prices. A market price emerges from the interaction between those competing preferences.

Economists use the term equilibrium for the price and quantity at which the amount buyers want to purchase equals the amount sellers want to offer.

This does not mean the price is fair, ideal, permanent, or acceptable to everyone. It simply means that, at that price, the quantity buyers want to purchase matches the quantity sellers want to sell.

When sellers cannot sell everything they offer, they may lower prices, reduce production, or both. When buyers compete for too few available goods, prices may rise and producers may have an incentive to supply more.

What does adjustment look like?

Imagine a farmers' market where strawberries normally sell for $4 a basket. After unusually bad weather, growers arrive with far fewer strawberries than usual. At $4, customers want to buy more baskets than are available.

Sellers may discover that they can charge $5 or $6 and still find buyers. As the price rises, some customers buy fewer strawberries, choose another fruit, or decide not to buy them. At the same time, the higher price gives growers a reason to bring as many strawberries as they reasonably can to market.

The price change is doing two things at once: discouraging some purchases and encouraging additional supply where additional supply is possible.

In real markets, adjustment may be slow or incomplete. Contracts, regulations, limited competition, production delays, imperfect information, and other conditions can affect how quickly—or whether—a market reaches equilibrium.

When Supply or Demand Changes

This is one of the most important—and most easily misunderstood—parts of supply-and-demand analysis. Economists distinguish between responding to a change in a product's price and a change in demand or supply itself.

A price change does not necessarily mean demand changed.

Suppose apples become cheaper and shoppers respond by buying more apples. Economists call that an increase in quantity demanded, not an increase in demand. Buyers are responding to the lower price.

Now suppose apples remain the same price, but new information leads more people to want apples. At every possible price, buyers are willing to purchase more than before. That is an increase in demand.

The same distinction applies to supply.

If the market price of tomatoes rises and farmers bring more tomatoes to market, that is an increase in quantity supplied. Sellers are responding to the higher price.

If a new harvesting technology lowers production costs and farmers can profitably supply more tomatoes at every price, supply itself has increased.

Common causes of changes in demand

• Consumer income.
• Tastes and preferences.
• Population and demographics.
• Prices of substitutes or related products.
• Expectations about future prices, employment, or income.

Common causes of changes in supply

• Wages, materials, energy, financing, and other production costs.
• Technology and production methods.
• Entry or exit of producers.
• Weather, disease, or natural disasters.
• Taxes, subsidies, regulations, and other public policies.
• Expectations about future market conditions.

Prices as Signals

Prices do more than determine how much buyers pay. In a market economy, changing prices can communicate information and influence behavior.

A rising price may signal that a product has become scarcer or that demand has increased. Buyers may respond by purchasing less, delaying a purchase, or looking for substitutes. Producers may respond by trying to increase supply.

A falling price may signal weaker demand or greater supply. Buyers may purchase more, while producers may reduce output or shift resources elsewhere.

No single buyer or seller needs to understand every reason behind a price change for the price to affect their decisions. This coordinating role of prices is one reason markets can organize large amounts of economic activity without a central authority directing every exchange.

Supply and Demand in the Real World

Real markets often involve several changes at once, but supply and demand can still help us organize the questions we should ask.

Case 1: Eggs after a disease outbreak

Suppose a disease outbreak forces poultry farms to destroy large numbers of laying hens. Consumers may want roughly the same number of eggs as before, but producers cannot supply as many. That is primarily a decrease in supply.

With fewer eggs available, prices tend to rise. The higher price may cause households and restaurants to buy fewer eggs or substitute other foods. Producers may eventually rebuild flocks, but that takes time.

Case 2: Housing in a growing community

Imagine a region attracting new residents because jobs are plentiful and the area is desirable. More households compete for homes and apartments. Housing demand increases.

Higher prices and rents can encourage builders to add housing, but supply cannot usually respond quickly. Land may be scarce. Labor and materials may be expensive. Interest rates affect financing. Zoning, permitting, infrastructure requirements, and community opposition can delay or limit construction.

If demand grows faster than supply can respond, prices can remain high for a long time. This illustrates why the speed and flexibility of supply matter.

Case 3: Gasoline

Gasoline prices can change because of conditions far from the local gas station. A disruption in crude-oil production or a refinery outage can restrict supply. Demand also changes with travel patterns and economic activity.

In the short run, many drivers have few alternatives and continue buying nearly as much gasoline when prices rise. Over a longer period, they may buy more fuel-efficient vehicles, change commuting patterns, or use other transportation. Buyers often respond more strongly when they have more time and alternatives.

Why Some Prices Change More Than Others

Buyers and sellers do not respond equally to every price change. Economists use the word elasticity to describe how strongly the quantity demanded or supplied responds when prices or other conditions change.

You do not need a formula to understand the basic idea.

If one brand of cereal becomes much more expensive, shoppers can easily switch brands. Demand for that particular cereal may respond strongly. If electricity becomes more expensive, a household has fewer immediate alternatives. It can conserve somewhat, but it probably cannot stop using electricity.

Supply differs too. A restaurant may be able to add another shift relatively quickly. A city cannot create thousands of new apartments overnight.

This helps explain why a modest disruption can sometimes produce a large price change: when buyers have few substitutes and producers cannot quickly increase supply, price may do much of the adjusting.

What Supply and Demand Does Not Tell Us

Supply and demand is a model—a simplified way of examining one part of economic life. It is useful, but it should not be mistaken for a complete description of an economy.

Markets respond to purchasing power—not necessarily to need.

A market price helps determine who is willing and able to buy something. That can coordinate many ordinary purchases effectively, but it raises harder questions when the good is essential.

A household unable to afford an apartment contributes less effective demand to the housing market than a wealthier household, even though its need for housing may be greater. A patient facing an emergency may have little ability to compare hospitals or postpone treatment.

This does not mean supply and demand has stopped operating. It means that explaining how a market allocates goods is different from deciding whether the resulting allocation meets broader social goals.

Not every market is highly competitive.

A seller with few competitors may have greater ability to influence prices. Workers in a community with only one or two major employers may have fewer alternatives when negotiating wages. Consumers may lack the information needed to compare complicated products such as insurance or medical services.

Real-world markets may also be affected by:

• Market power: some sellers or buyers may have much more influence than others.
• Unequal income and wealth: people's ability to participate in markets differs.
• Incomplete information: buyers and sellers may not know everything relevant to a decision.
• External effects: a transaction may impose costs or create benefits for people who are not part of it.
• Government rules and institutions: laws, taxes, subsidies, regulations, and public programs shape many markets.
• Time: housing, energy, agriculture, and other forms of production may take months or years to respond to changing prices.

These complications do not make supply and demand useless. They tell us when the basic model is a good starting point and when we need additional tools.

Key Terms

Market

An arrangement through which buyers and sellers exchange goods, services, labor, or other things of value.

Demand

The quantities buyers are willing and able to purchase at different prices.

Quantity demanded

The amount buyers are willing and able to purchase at a particular price.

Supply

The quantities sellers are willing and able to offer at different prices.

Quantity supplied

The amount sellers are willing and able to offer at a particular price.

Equilibrium

The price and quantity at which quantity supplied equals quantity demanded.

Shortage

A situation in which buyers want to purchase more than sellers offer at the current price.

Surplus

A situation in which sellers offer more than buyers want to purchase at the current price.

Elasticity

How strongly buyers or sellers respond to changes in price or other market conditions.