Demand and supply are basic concepts in economic analysis. This is because economics is fundamentally concerned with ends and means. The quantities of various goods demanded are expected to bring satisfaction of different wants or ends, the supply of these goods is conditioned by the availability or scarcity of resources which act as the means of production. Both the terms ‘demand’ and ‘supply’ have technical implications. By demand, we mean the quantity of any commodity that ‘buyers are willing and have the ability to buy.’ Both the conditions must be satisfied together before goods can be demanded. One who smokes wishes to purchase cigarettes but he must have enough money or resources to do so. Similarly, a quantity of a commodity is said to be supplied only when a seller is willing to sell it at the market price.

The two concepts of demand and supply are, however, relative in nature and conveniently interchangeable. For example, a person may visit a distant wholesale market and purchase 50 small cans of beer at a somewhat lower price than what he would have paid in the local market. Therefore 50 cans of beer can be said to be his demand for the commodity. On his way home he meets a friend B who requests for 10 cans of beer at a particular price. If the bargain is acceptable, A will sell 10 cans to B, which will consist of his (that is A’s) ‘supply’ and the remaining 40 cans will then be his demand. Later on if a close relative of A (say C) requests him to part with 5 cans of beer on a ‘no profit no loss’ basis, then that becomes a further part of his ‘supply’ and his demand is reduced to 35 cans of beer. Similarly a shopkeeper who begins with 200 cans of beer (which is his supply) may retain 10 cans for himself and for his family members (this is known as self-consumption). In that case, his supply is reduced to 190 cans and demand would be 10 cans.

Finally demand and supply are mutually opposing concepts, in the sense that demand is an inverse (falling) function of the price, while supply is a direct (rising) function of the price. This is explained in the following sections.

Demand Schedule, Function and Law

D(demand) qd	Schedule P
10	0
8	1
4	2
1	3
0	4

Demand Schedule : The various quantities demanded of a particular commodity are presented here in a schedule. At arbitrarily chosen prices, the quantity of a commodity an individual consumer is expected to demand, is explained by the schedule. Since quantity demanded (q_d) depends on the relevant prices of goods, the two can be expressed in the form of an algebraic function as well. The schedule shows that as price goes on rising (from zero to 4) the quantity demanded goes on falling (from 10 to zero).

The scheduled information has been presented in the form of a demand curve in Figure 2 (below). In the figure, the units of quantity of the goods have been measured along the horizontal axis (OX) and the respective prices have been shown along the vertical axis (OY). The curve intersects OY axis at point A which shows highest price at which quantity demanded is zero. On the contrary the curve intersects OX axis at point B showing largest quantity demanded where price is zero. Both OA and OB are said to be intercept quantities when one of the variables assumes zero value. Note that demand curve is sloping downward. This follows the law of demand (given below). But the demand curve of such a shape is obvious from the fact that quantities demanded and price in the demand schedule hold an inverse relationship.

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Law of demand: The law of demand explains the inverse relation between quantity and price in general. It can be stated as follows:

“ (other things remaining equal), the quantity of a good demanded will rise (expand) with every fall in its price and the quantity of a good demanded will fall (contract) with every rise in its price.”

Supply Schedule: Just as goods are demanded by consumers, they are supplied by manufacturers or sellers. At any point of time quantity supplied by them is a function of the market price. Several such prices can be related to the relevant quantities supplied: this would give the supply schedule. In the given schedule, as price of the goods rises (from zero to 3) the quantity supplied also rises (from zero to 6 units).

Supply Schedule
qs	P
0	0
2	1
4	2
6	3

(B) Supply Function: Supply is a direct function of the price and it rises or falls with the price. This is because the law of supply is based on the behavior of the cost of production. Assuming that manufacturers begin at the point where cost of production is minimal any further production and supply of goods can be possible only at an increasing additional or marginal cost per unit. Hence they can afford to supply more only at a rising price. Further, logically any seller would be willing to sell more goods if the price were to rise.

Law of Supply: The law of supply can be stated as follows:

“ the quantity of a good supplied will rise (expand) with every rise in its price and the quantity of a good supplied will fall (contract) with every fall in its price.”

the graphical representation (the supply curve) of the supply schedule. It begins at the point of origin where both quantity supplied and price are zero in value, and then it continuously rises upwards. This upward sloping curve indicates the positive relationship between supply and price: there is a rise in the quantity supplied with every successive rise in the price.