Change in supply means the shift of supply curve. With increase in supply, supply curve shifts to the right and with decrease in supply, the supply curve shifts to the left. The following factors cause a change in supply:

(i) Technological Change: When there is technological improvement, output is produced at lower cost. Lower cost of production increases the supply of the commodity. The supply curve shifts to the right.

(ii) Price of Other Goods: When price of a substitute good increases, the quantity supplied of the concerned good decreases and there is backward shift of the supply curve. Supply curve shifts forward in case price of the substitute good decreases.

(iii) Price of Factors of Production: If factor price decreases, cost of production also decreases. Accordingly, supply increases and the supply curve shifts to the right. If factor price increases, supply tends to decline and there is a backward shift in supply curve.

(iv) Number of Firms: Increase in the number of firms implies increase in market supply and conversely, decrease in number of firms reduces the market supply of the commodity.