Supply

Welcome to the World of Supply!

In the previous chapter, we looked at the market from the perspective of the buyer (Demand). Now, it’s time to switch seats and look through the eyes of the producers and firms. Why do businesses choose to make what they make, and how do they decide how much to sell? Understanding Supply is essential for figuring out how markets set prices and allocate resources.

Don't worry if this seems a bit "all about business" at first—it's actually very logical. Think of yourself as a seller on an app like Vinted or Depop. If you could sell a pair of shoes for £100 instead of £10, would you be more or less keen to list them? That's the heart of supply!

1. What is Supply?

Supply is the quantity of a good or service that a producer is willing and able to provide to the market at a given price, at a given time.

The Law of Supply

The Law of Supply states that there is a positive (direct) relationship between price and quantity supplied.
As the Price (\(P\)) of a product rises, the Quantity Supplied (\(QS\)) also rises.
As the Price (\(P\)) falls, the Quantity Supplied (\(QS\)) falls.

Why does this happen?
1. Profit Motive: If the price is higher, firms earn more profit per unit, so they want to sell more.
2. Cost of Production: Producing more often costs more (e.g., paying staff overtime). A higher price helps cover these extra costs.

Quick Review:
- Demand = Downward sloping (Consumers like low prices)
- Supply = Skyward sloping (Producers like high prices)

2. Individual and Market Supply

It is important to distinguish between a single business and the whole industry.

Individual Supply: The supply of one single firm (e.g., your local bakery).
Market Supply: The total supply of all firms in the market combined (e.g., every bakery in the UK).

To calculate Market Supply, we use Horizontal Summation. This means we add up the quantities supplied by every firm at each price level.

Example: If at £1, Firm A supplies 10 loaves and Firm B supplies 15 loaves, the Market Supply at £1 is \(10 + 15 = 25\) loaves.

3. Movements Along the Supply Curve

A movement along the curve only happens when the Price of the good itself changes. We call this a change in the Quantity Supplied.

Extension of Supply

When the price increases, producers move up the curve to a higher quantity. This is an extension.

Contraction of Supply

When the price decreases, producers move down the curve to a lower quantity. This is a contraction.

Common Mistake to Avoid: Never say "Supply increased" when you mean "Quantity Supplied increased." If only the price changed, it’s a movement, not a shift!

4. Shifts of the Supply Curve

A shift occurs when a non-price factor changes. This means that even if the price stays the same, firms want to sell more (or less) than before. This is called a Change in Supply.

Shift to the Right: Increase in supply (Producers provide more at every price).
Shift to the Left: Decrease in supply (Producers provide less at every price).

Memory Aid: PINTSWC

Use this mnemonic to remember why the Supply curve might shift:

P - Productivity: If workers become more efficient, costs fall, and supply shifts Right.
I - Indirect Taxes: If the government increases taxes (like VAT), it costs more to produce, so supply shifts Left.
N - Number of Firms: More businesses entering the market means market supply shifts Right.
T - Technology: Better machinery makes production cheaper and faster—supply shifts Right.
S - Subsidies: Government grants to firms lower their costs, shifting supply Right.
W - Weather: Particularly for farming! A drought will shift the supply of wheat Left.
C - Costs of Production: If wages or raw material prices (like electricity) go up, supply shifts Left.

Key Takeaway: If it makes production cheaper or easier, supply shifts Right. If it makes it expensive or harder, supply shifts Left.

5. Joint and Competitive Supply

Sometimes the supply of one product is linked to the supply of another.

Joint Supply

This happens when the production of one good automatically produces another as a "by-product."
Example: Beef and Leather. If the price of beef goes up, farmers raise more cattle. As a result, the supply of leather automatically increases too.

Competitive Supply

This happens when a firm can use its resources (like land or raw materials) to produce one of two different things.
Example: A farmer has one field. They can grow Wheat OR Barley. If the price of Wheat goes up, the farmer will use the land for Wheat. Therefore, the Supply of Barley falls because the resources were diverted.

Did you know?
Biofuels are a great example of competitive supply. As the demand (and price) for biofuels rose, farmers stopped growing as much food to grow fuel crops instead. This caused the supply of food to shift left and prices to rise!

6. Summary Quick-Check

Before moving on to the next chapter, make sure you can answer these:

1. Does the supply curve slope upwards or downwards? (Upwards)
2. What is the only thing that causes a movement along the curve? (Price)
3. If the government gives a subsidy to a firm, which way does the curve shift? (Right)
4. What is the difference between joint and competitive supply? (Joint = produced together; Competitive = produced instead of each other).

Great job! You've mastered the basics of Supply. Next, we will look at "Consumer and Producer Surplus" to see how both sides of the market benefit from trading.