The definition and law of supply

Supply describes how much of a product or service producers are prepared to make available at different price levels over a set period, assuming other factors remain unchanged.

The law of supply

The law of supply explains that there is a positive link between the price of a product and the amount producers are willing to provide in a given timeframe. When the price goes up, firms tend to supply more because it becomes more profitable to do so, provided other conditions stay the same.

Features of the supply curve

A supply curve is a graphical representation that illustrates the connection between a product's price and the quantity that firms are willing to supply during a specific period.

Key characteristics of supply curves

• Axes and shape - Price appears on the vertical axis, while quantity supplied is on the horizontal axis. The curve slopes upwards from left to right, reflecting the positive relationship where higher prices encourage greater supply.
• Individual supply curve - This shows the supply from a single firm at various prices.
• Market supply curve - This combines the supply from all firms in an industry. It is created by summing the quantities each producer offers at every price level.
• Example of market supply calculation - Suppose an industry has 75 similar companies, and each is ready to supply 250 units monthly at £12 per unit. The total market supply at that price would be 18,750 units per month.

Non-price determinants that shift the supply curve

Several factors besides the product's own price can influence the amount supplied. These cause the entire supply curve to move, either increasing or decreasing the quantity available at every price.

Changes in costs of factors of production

Higher costs for inputs, such as increased wages for workers or rising prices for materials, make production more expensive. This reduces supply, shifting the curve leftwards, meaning firms offer fewer units at each price or require higher prices to maintain the same output.

Prices of related goods

• Goods in joint supply - These are items produced together, like beef and leather from cattle farming. If the price of beef increases, farmers produce more, which also boosts leather supply, shifting its curve rightwards.
• Goods in competitive supply - These compete for the same resources, such as corn and soybeans on limited farmland. A rise in corn prices might lead farmers to grow more corn and less soybeans, shifting the soybean supply curve leftwards.

Indirect taxes and subsidies

• Indirect taxes are charges imposed by the government on each unit produced, raising costs and decreasing supply (leftward shift).
• Subsidies are government payments per unit produced, lowering costs and increasing supply (rightward shift).

Expectations of future price changes

If firms anticipate higher prices ahead, they might hold back current supply to sell later at better rates or expand production capacity. This temporarily decreases supply, shifting the curve leftwards in the short term.

Changes in technology

Advances in technology enable firms to produce more efficiently, reducing costs per unit and allowing greater output at the same price. This increases supply, shifting the curve rightwards.

Number of firms

An increase in the number of producers in a market expands overall supply, shifting the curve rightwards as more units are available at each price. Conversely, if firms leave the market, supply decreases, shifting the curve leftwards.

Distinguishing between movements along and shifts of the supply curve

Movements along the supply curve

These happen solely due to alterations in the product's own price. For example, if the price rises, firms move up along the curve and supply more; if it falls, they move down and supply less.

Shifts of the supply curve

These occur when non-price factors change, affecting supply at all prices. A rightward shift indicates an increase in supply, where more is offered at every price. A leftward shift shows a decrease, with less offered at every price.