1. Population: It is assumed that the population of whatever unit considered e.g family, nation, etc. remains the same, when the change in price takes place. It is also assumed that the age and sex composition of population remains the same during the process of consumption. ( during application of the law ).
2. Customs, tastes, preferences, habits of consumers remain constant: Any change in this will affect the change in demand resulting from the change in price e.g. If the price of a product decrease, the demand for it may not increase if the product has gone out of fashion.
3. Availability of substitutes and their price remains constant : If the number of substitutes available remains constant but price falls, the demand for the product may not increase with a fall in its price as the fall in the price of the substitute may be more than that in price of the product and vice versa.
4. Expectations of a consumer about future prices remain constant: If the price of the product falls and the consumer expects a further decrease in price, his demand for the product may not immediately increase and vice versa.
5. Quantity of money in circulation remains constant: In other word the purchasing capacity remains constant during the process of consumption. (during application of the law ).
6. Availability and prices of all other goods (complements and substitutes) remain constant: If the price of any other good falls, people will switch over to that good and hence demand for the first good may not increase in spite of a decrease in price.
7] No change in technique of production – A change in technique of production would affect the cost of production and therefore the price. This in turn will influence demand, Therefore technique of production is assumed to be constant.
8] Normal goods – It is assumed hat consumers generally demand normal goods, not inferior or prestige goods.
9. Income of the consumer remains constant – i.e. money income and real income during the process of consumption. (during application of the law).
10. Distribution of income and wealth remains constant – – If the distribution of income and wealth is equal, during application of the law
11. Propensity to consume – If propensity to consume is high people spend a larger proportion of their income on consumption and therefore demand increases
12. Level of tax and tax structure – does not change i.e. income tax, wealth tax, sales tax, various subsidies etc.
13. Climate and weather conditions remain constant. – E.g. demand for some goods will be affected. E.g. air conditioners, rain coats etc.