Introduction to Supply
Welcome to the world of producers! So far, you might have looked at why consumers buy things (Demand). Now, we are flipping the coin to look at the people who make and sell products: the suppliers. Understanding supply is vital because it explains how firms decide how much to produce and what price they need to keep their businesses running. Don't worry if it seems a bit technical at first—by the end of these notes, you’ll see that supply is mostly just common sense from a business owner’s perspective!
1. What is Supply?
Supply is the quantity of a good or service that producers are willing and able to provide to the market at a given price in a given time period. It’s not just about what a factory *can* make; it’s about what they are actually ready to put on the shelves to sell.
The Law of Supply
There is a positive relationship between price and quantity supplied. In simple terms:
- When the Price goes Up, the Quantity Supplied goes Up.
- When the Price goes Down, the Quantity Supplied goes Down.
Why does this happen? Imagine you own a bakery. If the price of a loaf of bread rises from £1 to £5, you’ll want to bake as much bread as possible because you can make more profit. If the price drops to 10p, you might not even cover your costs, so you'll produce very little.
Did you know? Economists assume that the main goal of most firms is profit maximisation. This is why they react so strongly to price changes!
Key Takeaway: The supply curve always slopes upwards (from left to right) because higher prices provide a profit incentive for firms to produce more.
2. Individual and Market Supply
It is important to distinguish between one single business and the whole industry.
- Individual Supply: The supply of an individual producer (e.g., one local coffee shop).
- Market Supply: The sum of all the individual supplies of all firms in the market (e.g., every coffee shop in the UK added together).
To find the market supply, you simply add up the quantities supplied by every firm at each price level.
Key Takeaway: Market supply is just the "big picture" version of individual supply.
3. Joint and Competitive Supply
Sometimes, producing one thing affects the production of another. This is a common area where students get confused, so let’s break it down simply.
Joint Supply
This happens when the production of one good automatically leads to the production of another. They are "by-products" of each other.
Example: If a farmer produces more beef, they automatically produce more leather (cowhide). You can’t get one without the other!
Competitive Supply
This happens when a firm can use its resources to produce either Good A or Good B. If they produce more of A, they must produce less of B because they use the same raw materials or land.
Example: A farmer has one field. They can grow wheat or barley. If the price of wheat rises, they will grow more wheat and less barley. The two goods are "competing" for the same field.
Key Takeaway: Joint supply means "buy one, get one produced free." Competitive supply means "it's either one or the other."
4. Movements Along the Supply Curve
A movement along the curve only happens when the Price of the good itself changes. Nothing else!
- Extension of Supply: When the price rises, and the quantity supplied increases. You move up the curve.
- Contraction of Supply: When the price falls, and the quantity supplied decreases. You move down the curve.
Common Mistake to Avoid: Never say the "supply changed" if only the price changed. Instead, say the "quantity supplied" changed. "Supply" refers to the whole curve; "Quantity Supplied" refers to a specific point on it.
Quick Review:
Price Change = Movement (Extension/Contraction).
Non-Price Change = Shift (Increase/Decrease).
5. Shifts of the Supply Curve
A shift happens when something other than price changes. This means that at the same price, firms are now willing to sell more (or less) than before.
- Shift to the Right: Increase in supply (more is supplied at every price).
- Shift to the Left: Decrease in supply (less is supplied at every price).
Factors that Shift the Supply Curve (The "PINTS WC" Mnemonic)
To remember why a supply curve might shift, use the mnemonic PINTS WC:
P - Productivity: If workers become more efficient, 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 shifts supply Right.
T - Technology: Better machinery reduces costs, shifting supply Right.
S - Subsidies: Government grants to firms reduce their costs, shifting supply Right.
W - Weather: Particularly for farming! A hurricane or drought shifts supply 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.
Summary Checklist
Before moving on, make sure you can answer these:
1. Why does the supply curve slope upwards? (Profit incentive!)
2. What is the difference between an extension and an increase in supply? (Price vs. Non-price factors).
3. Can you name three things that would shift the supply curve to the left? (Higher taxes, higher costs, bad weather).
4. How does Joint Supply differ from Competitive Supply? (By-products vs. Alternative uses of resources).
Don't worry if this feels like a lot to memorise! Practice drawing the diagrams. Once you can draw a shift to the right and label it correctly, the theory usually clicks into place.