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IB DP Economics Study Notes

2.2.1 Law of Supply

The Law of Supply is a cornerstone of economic theory, offering insights into the behaviour of producers when faced with changing market prices. It's crucial for understanding market dynamics and predicting producer responses to various economic scenarios.


At its core, the Law of Supply posits that, ceteris paribus (all other things being equal), as the price of a good or service increases, the quantity supplied of that good or service will also increase. Conversely, if the price decreases, the quantity supplied will decrease. This direct relationship between price and quantity supplied is foundational to the study of economics.

Graph of law of supply

A graph illustrating the upward sloping supply curve representing the law of supply.

Image courtesy of wallstreetmojo

Determinants of Supply

While the price is a pivotal factor in influencing supply, several other determinants can cause the supply curve to shift. These determinants, which are factors other than the product's price, play a vital role in determining the potential supply of a good or service. They include:

Production Costs

  • Raw Materials: The cost of raw materials can significantly influence the supply of a product. If the price of cotton rises, for instance, it might become more expensive to produce cotton shirts, leading to a decrease in the supply of these shirts at each price level.
  • Labour Costs: Wages and salaries paid to workers can impact the cost of production. If there's a surge in wages without a corresponding increase in worker productivity, the supply might decrease.
  • Energy Costs: The cost of energy, especially for industries heavily reliant on power, can influence supply. A spike in electricity prices can reduce the supply of goods from such industries.

To explore more about how these and other factors affect supply, refer to the detailed examination of Non-Price Determinants of Supply.

Technological Advancements

Technological progress can lead to more efficient production processes, allowing producers to produce more at a lower cost. For instance, the introduction of automation in car manufacturing can lead to more cars being produced at a reduced cost.

Number of Suppliers

The total number of suppliers in the market can influence supply. If new businesses enter an industry, it can increase competition and potentially boost the total supply of a particular good or service.

Expectations of Future Prices

Suppliers' perceptions of future market conditions can influence their current supply decisions. If they anticipate a price rise in the future, they might hold back some of their current stock to sell later at a higher price.

Government Policies

  • Taxes: Imposition of taxes can increase the cost of production. For instance, a new tax on leather might reduce the supply of leather goods. Learn more about how Taxation affects the supply of goods and services.
  • Subsidies: These are financial aids provided by the government to encourage production. A subsidy on solar panels can increase their supply in the market. For a closer look at how subsidies impact supply, visit the Subsidies page.
  • Regulations: Stringent regulations can increase the cost of compliance, potentially reducing supply. Conversely, deregulation can sometimes boost supply.

External Shocks

Unexpected events, such as natural disasters, wars, or geopolitical tensions, can disrupt production processes, leading to supply fluctuations. The impact of Negative Externalities of Production on supply is a critical aspect of understanding market dynamics.

Unknown block type "table", specify a component for it in the `components.types` option

A summary table of the determinants of supply.

Movement vs. Shift

Understanding the distinction between a movement along the supply curve and a shift in the supply curve is pivotal:

Movement Along the Supply Curve

This is a response to a change in the price of the good itself. For instance, if there's a surge in the demand for umbrellas due to forecasted rains, the price might rise. In response, umbrella manufacturers might increase their production, leading to a movement up the supply curve.

Graph of movement along supply curve

A graph illustrating the movement along the same supply curve.

Image courtesy of byjus

Shift in the Supply Curve

This is instigated by changes in any of the determinants of supply other than the good's own price. For example, if a new technology allows umbrellas to be produced at half the previous cost, suppliers can now offer more umbrellas at every price level, leading to a rightward shift in the supply curve. For further understanding of how supply curves can shift, consider the explanations on Changes in Equilibrium.

Graph of shift in supply curve

A graph illustrating the shifts in the supply curve.

Image courtesy of lumenlearning

In conclusion, the Law of Supply offers a lens through which we can analyse producer behaviour in response to changing market conditions. By understanding both the law itself and the various determinants of supply, students can gain a comprehensive insight into the intricate dance of market dynamics. As you progress in your studies, you'll find that these foundational concepts are integral to understanding more complex economic phenomena.


Globalisation can amplify or mitigate supply responses. With interconnected global markets, producers have access to a broader range of resources, technologies, and markets. If there's a surge in demand and prices in one country, producers from another country can increase their supply, potentially stabilising prices. On the flip side, a disruption in one part of the world, like a strike in a major port, can affect supply chains globally, impacting the supply of various goods. While the Law of Supply still holds at a fundamental level, globalisation introduces additional layers of complexity in how supply responds to price changes.

While the Law of Supply is a foundational concept in economics, there can be situations where producers don't respond to price changes as the law would predict. For instance, in the case of some luxury goods, producers might limit the quantity supplied even if the price rises to maintain exclusivity. Another example could be certain agricultural products; if farmers believe that increasing production significantly might lead to a future price crash, they might resist increasing supply even with rising prices. However, these are exceptions and not the norm.

Natural disasters can have a significant impact on the supply of goods and services. They can disrupt production processes, damage infrastructure, and reduce the availability of raw materials. For instance, if a major flood affects a rice-producing region, the immediate supply of rice might decrease due to damaged crops. This doesn't negate the Law of Supply but rather shifts the supply curve to the left, representing a decrease in supply at every price level. The law still holds, but the external shock from the natural disaster changes the starting conditions.

The term "law" in economic theory doesn't imply a legal statute but rather a fundamental principle or observed phenomenon that tends to hold true across various scenarios. The Law of Supply is termed a 'law' because it consistently observes that, all else being equal, producers are willing to offer more of a good for sale as its price increases. This consistent observation, both in theoretical models and real-world scenarios, gives it the status of a 'law' in economics.

Expectations about future market conditions can significantly influence current supply decisions. In volatile markets, where prices can swing dramatically, producers might adjust their current supply based on their expectations. For example, if oil producers expect future prices to skyrocket due to geopolitical tensions, they might reduce their current supply, hoping to sell later at higher prices. Conversely, if they expect future prices to plummet, they might increase their current supply to sell as much as possible before the price drop. This anticipatory behaviour can sometimes exacerbate market volatility.

Practice Questions

Explain the difference between a movement along the supply curve and a shift in the supply curve, providing an example for each.

A movement along the supply curve is a change in the quantity supplied due to a change in the price of the good itself. For instance, if the price of oranges increases, producers might supply more oranges, leading to a movement up the supply curve. On the other hand, a shift in the supply curve occurs due to changes in any of the determinants of supply other than the good's own price. For example, if a new farming technique allows for more efficient orange cultivation, the supply of oranges might increase at every price level, causing a rightward shift in the supply curve.

How do government policies, such as taxes and subsidies, influence the supply of a product? Provide examples to support your answer.

Government policies play a pivotal role in determining the supply of a product. Taxes increase the cost of production, potentially leading to a decrease in supply. For instance, if the government imposes a tax on the production of sugary drinks, it might lead to a reduced supply of these drinks in the market. Conversely, subsidies are financial aids provided by the government to encourage production. A subsidy on electric vehicles, for example, can reduce the cost of producing such vehicles, leading to an increase in their supply. Both policies, therefore, have direct implications on the cost of production and, consequently, the supply of goods and services in the market.

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Written by: Dave
Cambridge University - BA Hons Economics

Dave is a Cambridge Economics graduate with over 8 years of tutoring expertise in Economics & Business Studies. He crafts resources for A-Level, IB, & GCSE and excels at enhancing students' understanding & confidence in these subjects.

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