Four factors affecting demand are as follows:

 Consumers tastes and Preferences: Tastes and preferences depend on social customs, fashion, habits of people etc. which keeps on changing leading to change in customers’ taste and preferences. As a result, the demand for different goods changes. 

For example: consumers may switch over from cheaper old fashioned goods to costlier ‘mod’ goods.

The income of the consumer: Generally when the income of a consumer goes up, the demand . for a commodity also goes up and when income falls, the demand also falls in case of normal goods.

Price of related goods (i.e. of substitute goods and complementary goods): In the case of complementary goods like car and petrol, the demand for a commodity rises with a fall in the price of complementary good. In the case of substitute goods like tea and coffee, demand for a commodity falls with a fall in the price of other substitutes good.

The expectation of Change in the Price in Future: If the price of a certain commodity is expected to increase in the near future, then people will buy more of that commodity than what they normally buy. There exists a direct relationship between the expectation of change in the prices in future and change in demand in the current period.

For example: if the price of petrol is expected to rise in future, its present demand will increase.