Common giffen goods in life are expensive jewelry, cultural relics, calligraphy and painting. "Jia Xu Commodity" is named after Ji Fen, an Englishman. Ji Fen, an Englishman, found that when there was a famine in Ireland in 1845, the price of potatoes rose sharply, but the demand increased instead. It turned out that famine caused the Irish people's real income to drop. As a kind of low-grade food necessary for life, the decline in real income has forced human beings to increase their purchases of this kind of goods.

Everyone knows the law of demand, that is, the demand for goods is inversely proportional to its price when other conditions remain unchanged. However, there are some opposite situations in life. Goods whose demand is in direct proportion to the price are called "Jia Xu goods". The special feature of Giffin commodity is that its income effect exceeds its substitution effect. This is the special reason why Giffin's commodity demand curve inclines to the upper right. There are also examples of "goods made in Jia Xu" in our life, such as expensive jewelry, cultural relics, calligraphy and painting. The more expensive these goods are, the greater the demand, because the price of these goods has become a symbol of consumers' identity and status.

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1. We admit that the theoretical giffen commodity is the result of the superposition of income effect and substitution effect, then we admit that the theoretical giffen commodity can exist under the premise of "other conditions unchanged". The fundamental reason for its existence is caused by the characteristics of consumer utility function or indifference curve (preference characteristics). When the commodity set is two kinds of commodities, the indifference curve is seriously inclined to one axis, that is, when the absolute value of its slope reaches a certain level, the theoretical Giffen commodity appears. Ji Fen's discovery in those days was not simply a commodity phenomenon in Jia Xu.

2. In reality, the pure giffen commodity phenomenon is of course very rare.

First, in the years of extreme famine, under the given income conditions at that time, Jia Xu commodities will appear.

Second, for very high-end goods and special new products, there will be Ji Fen phenomenon, such as a new product, which most consumers don't understand. At this time, if you use a lower price as an ordinary substitute (for example, mechanical pencil instead of an ordinary pencil), the demand will be limited, but if you use a higher price as a high-end product, the demand will be more, and people will buy it as a status symbol. Therefore, the same commodity may be a Giffin commodity for some people, but it may be an ordinary commodity for others. This shows that when analyzing economic problems, we should clearly examine the time and space range of variable changes.