very different movement in prices, for the question of causal relations is a complicated one--from the change in prices that might accompany the same increase in the amount exchanged of same goods under other circumstances. Finally, the doctrine of the quantity theory that the price-level is a passive result of the other factors named: quantities of goods and money, and their respective velocities; that prices cannot initiate a change in the situation, will also be challenged. I shall undertake to show that the first change in the situation may appear in prices themselves, and that the quantities of goods exchanged, and of money, and their velocities, may then be altered to correspond with the change in prices. I shall further maintain, as against the whole spirit of the quantity theory, that it does not seize hold of essentials in the causes lying behind prices. I shall contend that the factors with which it deals, instead of being independent _foci_ to which converge the causes governing the price-level, and through which causation flows in one direction, are really not true "factors" at all, but rather are blanket names for highly complex and heterogeneous groups of facts concerning which few general statements are possible. Quantity of goods exchanged, for example, may be in some of its parts caused by rising prices, in others of its parts may be causing falling prices and is chiefly caused by _fluctuating_ prices. The net change in prices in this case is not the result of any one movement from "quantity of goods" as a whole. Changes in the price-level are not one result, but rather, are the mathematician's average of many changes, due to a host of causes, in many individual prices. The quantity theory is an effort to simplify phenomena highly complex. Of course, the simplification of complex phenomena in thought is a laudable scientific goal, but when the simplification goes so far as to group things only superficially related, and to leave out the really vital elements, it is worthless. Value theory, with all the value left out, is like Hamlet with no actor for the title role. Simplification in the explanation of general prices has gone as far as we can legitimately take it when we seek to summarize all the factors involved in the _foci_ of, on the one hand, the value of money, and, on the other hand, the values of the particular goods. The general price-level is an average of many concrete prices. Each of these individual prices has a concrete causal explanation. The _general_ price-level has, not a few simple causes, but an infinite host of causes. Indeed, the general price-level has no real existence. It is a convenient mathematical concept, by means of which we may summarize the multitude of concrete facts. It is useful as a device for measuring changes in the value of money, on the assumption that changes in the values of goods neutralize one another. This assumption is never strictly true, and often is demonstrably false.