Theory of Supply: Supply Function and Law of Supply | Economics

While demand focuses on the consumer, supply looks at the world through the lens of the producer. It explores the relationship between the price of a good and the quantity that businesses are willing to bring to market.

Supply Function

Supply function explains as to how the quantity supplied of a commodity changes on account of changes in determinants of supply. This function expresses the relationship between supply and price. It also gives us an idea that quantity of a commodity supplied varies directly with its price, other determinants of supply remaining constant. Supply and price has a positive relationship. Therefore, they move in the same direction.

It can be expressed as S(x) = f (Px).

Supply function:

Q(x) = f [Px, P1, P2, Pn………. f1, f2, fn……. T, O]

Here,

• Q(x) – quantity supplied of the commodity x
• P(x) – price of the commodity x
• P1, P2, Pn – price of other commodities
• f1, f2, fn – cost of production
• T – technology
• O – objective of supplier/firm

Law of Supply

Law of Supply states that other things remaining constant, the quantity supplied varies directly with the price of the commodity. It also explains that when price of a commodity increases, the supply expands and vice-versa. The relationship between supply and price is positive. Therefore, higher the price, larger is the supply; lower the price, lesser is the quantity supplied.

Assumptions of Law of Supply

Few assumptions related to Law of Supply are as follows:

1. Number of Firms in the Market Remains Constant - If new firms enter the industry, the total market supply would increase even if the price stays the same. To isolate the effect of price on a single curve, we assume the competition level is static.
2. No Change in the Level of Technology - Improved technology usually lowers production costs or increases efficiency. If tech improves, a seller might supply more even at a lower price, which would shift the entire supply curve rather than just moving along it.
3. Cost of Production Does not Change - This refers to the "input prices" (wages, raw materials, rent). If the cost of leather drops, a shoe manufacturer will produce more shoes at every price point because their profit margin has increased.
4. Rate of Production Remains Constant - This assumes there are no sudden shifts in the scale of production or sudden bottlenecks in the manufacturing process that would artificially limit how much a firm can output.
5. Prices of Related Goods remain Constant - If a farmer grows wheat and the price of corn (a related good) suddenly skyrockets, the farmer might switch to corn. We assume the prices of these "substitutes in production" stay still so the seller isn't tempted away.
6. No Change in Climatic Conditions - This is particularly vital for agricultural products. A sudden drought or a perfect harvest would change the supply regardless of the market price.
7. No Expectation of Future Price Changes - The seller does not expect any drastic change in the price of the commodity in near future. If a seller thinks the price will double next week, they will hoard their stock today (decreasing current supply) even if today's price is high.
8. No Change in Government Policies - This includes taxes and subsidies. If the government slaps a heavy "sin tax" on a product, the supply will likely drop because it becomes less profitable for the seller, regardless of the retail price.

Importance of Law of Supply

Understanding the law of supply is beneficial for a person for many reasons such as:

1. Price Determination: The law of supply, along with the law of demand, is a key factor in determining market prices. It helps explain how the interaction between buyers and sellers in a market leads to price equilibrium.
2. Production and Supply Decisions: Businesses use the law of supply to guide their production decisions. When prices are high, businesses are motivated to produce and supply more to maximize profits. Conversely, when prices are low, they may reduce production to avoid losses.
3. Market Efficiency: The law of supply helps ensure that markets are relatively efficient in allocating resources. It helps to avoid surpluses (too much supply) and shortages (too little supply), by guiding producers to adjust their output based on price signals.
4. Forecasting and Planning: Businesses and policymakers can use the law of supply to forecast how changes in price or other factors (like technology or government policies) might affect production and supply.
5. Understanding Market Dynamics: The law of supply provides insights into how producers respond to changes in market conditions.

Exceptions / Limitations of law of Supply

There are some situations under which the law of supply of goods is not applicable. It means that the supply of goods and the price of a commodity are not proportional. The exceptions to the law of supply are as follows:

1. Monopoly - In a monopoly, the seller is a price maker rather than a price taker. Because they control the entire market, they may deliberately restrict supply even when prices are high to maintain "scarcity value" and maximize long-term profits. Unlike a competitive market, there is no direct, positive correlation between price and the quantity offered.
2. Closure of Business (Business Liquidation) - When a firm faces bankruptcy or closure, the primary objective shifts from profit maximization to liquidity. The seller will flood the market with inventory at drastically reduced prices to clear stock and recover whatever capital they can. Here, supply increases while prices decrease, which is the exact opposite of the Law of Supply.
3. Perishable Goods - For goods with a limited lifespan (e.g., vegetables, milk, or fish), supply becomes perfectly inelastic. Sellers cannot "hold back" stock to wait for higher prices because the goods will spoil. Therefore, they may supply the same (or even higher) quantity as prices fall to avoid a total loss.
4. Market Competition and "Dump Pricing" - In highly competitive environments, or when a company enters a new market, they may engage in predatory pricing or "dumping." They increase the quantity supplied at lower prices to drive out competitors or gain a foothold. This strategic behaviour ignores the standard price-to-supply relationship.
5. Agricultural Products - The supply of agricultural products is dictated by natural factors and time lags. Because land is a fixed resource and crops take months to grow, a sudden spike in price cannot trigger an immediate increase in supply. Furthermore, if a harvest is poor due to weather, supply will fall regardless of how high the price rises.
6. Clearance of Obsolete (Out-of-Fashion) Goods - When goods become technologically obsolete or go out of fashion, their marginal utility drops. Retailers often increase the supply of these items (clearance sales) while simultaneously slashing prices to make room for new trends. The downward price movement is accompanied by an upward supply movement.
7. Rare and Artistic Goods - The goods that are precious or artistic, generally have a limited supply. The supply of these goods cannot be raised according to the rising prices or demand. Hence, if the price of the goods increases, the supply of such rare goods cannot be raised. 

Supply Schedule

Supply schedule is a table that shows the relationship between the price of a good or service and the quantity suppliers are willing and able to produce and sell at those various prices over a specific period. 

A supply schedule has two main types:

1. Individual Supply Schedule: This shows the quantity of a good that a single producer or firm is willing to offer at different prices during a specific time period, assuming all other factors remain constant.
2. Market Supply Schedule: This represents the total quantity of a good that all producers in a market are willing to supply at various prices during a given period, essentially the sum of all individual supply schedules.

Sample Supply Schedule:

Supply Curve

If we show the supply schedule graphically, we get the supply curve. It shows the maximum quantities per unit of time that producers will supply at various prices. The Supply Curve slopes upward from left to right.

Reasons for upward sloping of Supply Curve:

The supply curve slopes upward from left to right primarily due to the relationship between price and quantity supplied. There is a positive relationship between the price and quantity supplied. Here are the main reasons: -

1. Profit Motive - When the price of a product increases, producers can earn more profit per unit sold. This encourages them to increase production to take advantage of the higher profitability. 
2. Increasing Marginal Costs - As a company expands its production, it may need to use more resources (labour, materials, etc.), which can lead to higher costs for each additional unit produced. To justify the increased production costs, producers need to sell their goods at a higher price. 
3. Diminishing Marginal Returns - As a business increases inputs (like labor or capital), it may experience diminishing marginal returns, meaning each additional unit of input adds less and less to total output. To offset the diminishing returns and maintain profitability, firms need to charge higher prices as they produce more.
4. Market Dynamics - When demand for a product increases, it drives up the market price. This higher price incentivizes producers to increase their supply to meet the growing demand and capitalize on the higher prices. Changes in price cause movements along the supply curve. For example, if the price of a good increases, the quantity supplied will increase, moving along the existing supply curve.

Factors Affecting Supply / Cause of Change in Supply

Supply gets affected due to a variety of factors such as: -

1. Production Costs - Changes in the cost of raw materials, labour, or other inputs, directly affect production costs. For example, if the price of coffee beans increases, the cost of producing coffee will also increase, potentially leading to a decrease in supply. Advancements in technology can lower production costs by making processes more efficient or enabling the use of new materials. This can lead to an increase in supply. 
2. Number of Sellers – If more firms enter a market, the overall supply will increase. Conversely, if firms exit the market, the supply will decrease. Increased competition among sellers can also influence the overall supply.
3. Government policies -  Taxes on production can increase costs and decrease supply, while subsidies can lower costs and increase supply. 
4. Speculations - If sellers expect future prices to be higher, they may decrease current supply to sell more later. Conversely, if they expect prices to fall, they may increase current supply to avoid losses.
5. Price of Related Goods - If the price of a substitute good increases, sellers may shift production towards that good, potentially decreasing the supply of the original product. If the price of a complementary good increases, the supply of the original product may also increase as it becomes more profitable to produce both together.

Change in Supply

Change in the supply refers to the movement along the same supply curve due to change in price of the commodity. However, when the change in supply is associated with change in factors like cost of production, technology, innovation etc., it causes a shift of supply curve upwards & downwards.

When the prices of inputs like labour and raw materials used for the production of a commodity declines, it results in lowering the cost of production, which will induce the producer to produce more and make available a greater quantity of the commodity in the market. This reduction in price of inputs leads to increase in supply of commodity, which cause the entire supply curve to shift towards the right (upward movement).

Different Kind of Changes in Supply:

1. Increase in Supply
2. Decrease in Supply
3. Extension/Expansion of Supply
4. Contraction of Supply

Difference between Increase in Supply and Decrease in Supply:

Difference between Extension of Supply and Contraction of Supply:

Difference between Increase in Supply and Extension of Supply:

Difference between Decrease in Supply and Contraction of Supply:

Note: - In all the differentiations above, do make diagram of each (increase, decrease, extension, contraction) in each distinction, depicting their movement.