There can be a general rise or fall of prices. Goods in general, other than money, may rise in value, while money remains constant in value. This would mean a rise in prices. Or, money may fall in value while goods in general are stationary in value. This would also mean a rise in prices. In either case, more money would be given for other goods, and the ratio between the value of the money unit and the value of other goods would have altered adversely to money. There are writers to whom the term, value of money, means merely the average of prices (or the reciprocal of the average of prices). For them, a rise in the average of prices is, _ipso facto_, a fall in the value of money. This view will receive repeated attention in later chapters. The view maintained in the present book is that the value of money is a quality of money, that quality which money shares with other forms of wealth, which lies behind, and causally explains, the exchange relations into which money enters. Every price implies _two_ values, the value of the money-unit and the value of the unit of the good in question. Value is prior to _exchange_. Value is not to be defined as "power in exchange." Certain writers[7] who see the need of a quantitative value, which can be attributed to goods as a quality, still cling to the notion that value is relative, that two goods must exist before one value can exist, and that value is "power in exchange," or "purchasing power." The power is conceived of as something more than the fact of exchange, and as a cause of the exchange relations, but is, none the less, defined in terms of exchange. This position, however, does not really advance the analysis. It is a verbal solution of difficulties merely. To say that goods command a price because they have power in exchange is like saying that opium puts men to sleep because it has a dormitive power. Physicians now recognize that this is no solution of difficulties, that it is merely a repetition of the problem in other words. If we wish to explain exchange, we must seek the explanation in something anterior to exchange. If value is to be distinguished from ratio of exchange at all, it cannot be defined as "power in exchange."