The definition of supply

Supply refers to the total amount of a good or service that producers or sellers are prepared and capable of offering for sale at various price levels within a set timeframe, assuming all other influencing factors stay the same.

The components of the supply definition

The definition of supply breaks down into several key elements that clarify what it means in economic terms.

Key elements in the supply definition

• Quantity - The specific numerical volume of the good or service that suppliers aim to provide.
• Product - Any type of item available in the market, which could include physical goods, services, foreign currencies, or financial instruments.
• Suppliers - The individuals or organisations offering the product, which might include manufacturers, distributors, or other participants in the supply chain.
• Willing and able to sell at different prices - Suppliers increase the amount they offer as prices rise, creating a positive link between price and quantity supplied.
• Per period of time - Supply is always measured over a defined period, such as per day, week, or month, to make it meaningful.
• Ceteris paribus - This Latin phrase means 'other things being equal', ensuring that the analysis focuses solely on price changes while assuming no shifts in external factors like costs or regulations.

The supply curve and its characteristics

The supply curve is a visual tool that illustrates how the quantity supplied changes in response to different price levels. It is typically plotted on a graph with price on the vertical axis and quantity supplied on the horizontal axis.

The market supply schedule

A market supply schedule is a table that lists the total quantity of a product that all suppliers in a market are willing to offer at various price points.

Example market supply schedule for a product:

Main characteristics of the supply curve

• Positive relationship - The curve slopes upwards from left to right, indicating that as price rises, quantity supplied increases, and as price falls, quantity supplied decreases.
• Movements along the curve - Changes in the product's own price cause movements along the existing supply curve, such as an extension (increase in quantity supplied) when price goes up or a contraction (decrease in quantity supplied) when price goes down.
• Causal link - Price acts as the independent variable that directly influences the quantity supplied.
• Linear and continuous nature - The curve is often drawn as a straight line for ease, allowing for estimates of quantities at prices not explicitly listed in the schedule.
• Time-specific basis - The curve represents supply over a particular period, ensuring comparisons are consistent.

The factors that affect supply

Various non-price factors can influence the overall supply of a product, causing the entire supply curve to shift. A rightward shift indicates an increase in supply (more quantity at every price), while a leftward shift shows a decrease in supply (less quantity at every price).

Key factors influencing supply

• Costs of production - Increases in expenses like wages, energy prices, or transport fees raise overall costs, shifting the supply curve leftward as suppliers offer less at each price. Conversely, improved worker productivity or lower costs shift it rightward.
• Size and nature of the industry - Expansion in an industry, such as through new firms entering due to high profits, increases total supply and shifts the curve rightward.
• Changes in prices of other products - If the price of a competing or substitute product rises, suppliers may divert resources to it, reducing supply of the original product and shifting its curve leftward.
• Government policies - Taxes on production decrease supply by raising costs (leftward shift), while subsidies lower costs and encourage more supply (rightward shift).
• Other external factors - Events like adverse weather (e.g., droughts or storms affecting crops) can reduce agricultural supply, shifting the curve leftward, whereas favourable conditions increase it.