What is inferior goods?





We call the goods which decrease demand with increasing a income inferior oods.Usually the demand increase when a income increase.Such a goods is called superior goods.Then what is inferior goods,what is the condition which is inferior goods?

When a income increase at least,the demand of the goods(it notes A below) doesn't decrease.We need a condition to decrease demand.The condition is existence of the substitute(B too) which make up for a portion which decrease.that is following:
(1)when the price of A is equal to B,the utility of B is larger than A.
(2)When the utility of A is equal to B,The price of B is cheaper than A.
However the condition of both is proper generally,they don't relate the increase of a income or the decrease of it.To be inferior goods,the demand of B must increase and the demand of A must decrease only when a income increase.
The reason that the demand of B is small in that a income is small is that person doesn't have a income enough to buy B.Therefore B is the goods which is more expensive than A and more useful than A.

Therefore the condition of inferior goods is following:
(1) There is substitute.
(2) The substitute has high price than the goods.
(3) The substitute has high utility than the goods.






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