Substitution Effect

-  The  substitution effect is change in an item's consumption associated with the change in the price of the item, level of utility held constant.

-  When the price of item declines, substitution effect leads to an increase in the quantity of item demanded.

Income Effect

- The income effect is change in the consumption of an item brought by increase in purchasing power, with the price of item held constant.

- When income of person increases, the quantity demanded for product can increase or decrease.

-  Even with inferior goods, the income effect is sufficiently large to outweigh the substitution effect.