The Law of Demand — Statement, Demand Schedule and Demand Curve

The Law of Demand, most closely associated with Alfred Marshall, is one of the most fundamental generalisations in the whole of Economics. It states: other things remaining constant, the quantity demanded of a commodity varies inversely with its price — as the price of a commodity rises, the quantity demanded of it falls; as the price falls, the quantity demanded rises. The law describes only the direction of the relationship between price and quantity demanded; it says nothing by itself about the exact proportion by which quantity changes for a given change in price — that question belongs to the separate chapter on Elasticity of Demand.

Individual demand schedule. A demand schedule is a table listing the different quantities of a commodity a buyer is willing to purchase at different prices, over a given period, other things remaining the same. Consider a hypothetical individual demand schedule for mangoes:

As the price falls from Rs 100 to Rs 20 per kg, the quantity demanded steadily rises from 2 kg to 10 kg per week — exactly the inverse relationship the Law of Demand describes. A market demand schedule is obtained by adding together, at each price, the quantities demanded by every individual buyer in the market.

The demand curve is simply the graphical picture of a demand schedule — price is conventionally measured on the Y-axis and quantity demanded on the X-axis, and each price-quantity pair from the schedule is plotted as a point; joining the points gives the demand curve. …