How does the law of supply differ from the law of demand?

In one line

The rule

Law of Demand: All else being equal, as the price of a good or service decreases, the quantity demanded increases, and vice versa. (NCERT) Law of Supply: All else being equal, as the price of a good or service increases, the quantity supplied increases, and vice versa.

• Law of Demand formula: Qd = f(P) (Qd is quantity demanded, P is price)
• Law of Supply formula: Qs = f(P) (Qs is quantity supplied, P is price)

Let's understand it simply

Imagine you are at a cricket match. If the price of samosas drops from ₹20 to ₹10, more people rush to buy them. This is demand: buyers want more when it’s cheaper.

Now imagine you are the seller. If you can sell samosas for ₹30 each, you will want to make and sell more, because you earn more profit. This is supply: sellers want to sell more when the price is higher.

So, buyers and sellers think in opposite ways about price. Buyers like low prices. Sellers like high prices.

How it works

1. Law of Demand:
2. Price goes down.
3. More buyers can afford the item.
4. Quantity demanded goes up.
5. If price goes up, fewer buyers want it, so demand falls.

1. Law of Supply:
2. Price goes up.
3. Sellers see a chance to earn more.
4. They make or offer more of the item.
5. If price goes down, sellers offer less, as profit is lower.

The story behind it

The Law of Demand was noticed by early economists like Alfred Marshall in the late 1800s. He saw that people buy more when things are cheaper. The Law of Supply was also described by Marshall and others, who saw that businesses produce more when they can sell at higher prices.

One memorable detail: Marshall used simple diagrams (now called demand and supply curves) to show these ideas, making economics easier to understand for everyone.

Where you see it in real life

• Vegetable market:
• If tomatoes become cheap during the monsoon, more people buy them (law of demand).
• Farmers bring more tomatoes to sell if prices are high (law of supply).
• Mobile phones:
• When a new phone’s price drops, more students want to buy it (demand).
• Companies make more phones if they can sell them at a higher price (supply).
• Bus tickets during festivals:
• If ticket prices go up, fewer people travel (demand).
• More buses are run by operators to earn more (supply).
• Diwali sweets:
• Lower prices attract more buyers (demand).
• Sweet shops make extra sweets if prices are good (supply).
• Cycle repair shops:
• If repair charges go up, fewer people get repairs (demand).
• More mechanics open shops if they can earn more (supply).
• Online sales:
• Discounts increase buyers (demand).
• Sellers list more products when prices are high (supply).

Why it matters

• Business decisions: Shops use these laws to set prices and plan how much to stock.
• Government policy: Helps decide on taxes, subsidies, and price controls.
• Market balance: Explains how prices settle where demand and supply meet (equilibrium).
• Exams: Questions on demand and supply are common in economics papers.

Worked example

Let’s compare both laws with numbers:

Law of Demand:
Given: Price of apples drops from ₹100/kg to ₹80/kg
Step 1: Write the rule        As price falls, demand rises
Step 2: See the change        Quantity demanded rises from 50 kg to 70 kg
Step 3: Answer                Law of demand is seen: lower price, higher demand

Law of Supply:
Given: Price of apples rises from ₹100/kg to ₹120/kg
Step 1: Write the rule        As price rises, supply rises
Step 2: See the change        Farmers bring more apples to market, supply rises from 60 kg to 85 kg
Step 3: Answer                Law of supply is seen: higher price, higher supply

Common mistakes

• Mixing up demand and supply: Remember, demand is about buyers, supply is about sellers.
• Thinking both increase with price: Only supply increases with price; demand decreases.
• Forgetting 'all else being equal': These laws work only if other factors (like income, taste, weather) stay the same.
• Assuming the laws work for every good: Some rare goods (like medicines) may not follow these laws exactly.

Remember it

Demand goes DOWN with price UP; supply goes UP with price UP.

Comparison Table

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