There are several agreed product categories, as not all products seem to give rise to the same consumer behaviour when it comes to demand.
Goods/services that see a rise in their aggregate demand as incomes (this is seen to be real purchasing power) rise are seen as normal products. Family Cars would fit this category.
Goods/services that see a decrease in their aggregate demand as incomes rise, are seen as inferior products. Examples of this might be junk food, because as purchasing power increases then consumers might very well decide to purchase better quality food and decrease their fast food purchases.
In this instance, there is likely to still be an overal increase in demand due to a larger positive substitution effect than negative income effect.
There is a special class of inferior products, that shows increased demand as prices rise.
An example here, would be in 19th Century Ireland. When the price of potatoes rose people were unable to purchase the more expensive meat and fish and so purchased more potatoes. This is actually one of the main causes to famine and malnutrition in developing world.
So in this instance the income effect of price change far outweighs the substitution effect seen.
This is the Luxury Goods classification, and shows that as price increase so does the demand. Normally there is 0 demand up to a price, and then demand increase rapidly. This is known as the ‘snob effect’.