Criticism of this theory is almost superfluous. There are elements in Wieser's discussion, not here presented, which have very considerable importance, and which will be presented in a later chapter when the criticism of the quantity theory is taken up. Wieser deals some heavy blows to the quantity theory. But his constructive doctrine presents the clearest possible case of the Austrian circle. The value of money depends, not on its subjective use-value, its own marginal utility--it has none. The value of money depends on its subjective value in exchange, the marginal utility of the goods which are exchanged for it. But these depend on prices. And prices depend, in part, on the value of money itself! This circle, present in every form of the Austrian theory which seeks a causal explanation of value and prices by means of marginal utility,[73] though often less obviously present, is here quite glaring. The distinction between volume of money income and quantity of money is, on the other hand, an important one, and will be emphasized when the quantity theory is taken up.[74] One further point in Wieser's doctrine calls for comment. It is strange indeed to find an Austrian seeing in a rise in money costs a _cause_ of a general rise in prices. The Austrian doctrine is rather that rising money costs are _reflections_ of rising general prices. Wieser's doctrine that the extension of the money economy to rural regions, compelling the farmer to reckon all his costs in money and so to raise his prices, has been adequately criticised by von Mises, who points out that Wieser sees only half the phenomenon; that eggs and butter are, indeed, higher in price in the rural region when it comes into contact with the city, but that they are correspondingly lower in the city from the same cause. On the other hand, the doctrine of costs is not the whole point in Wieser's notion of the extension of the money economy as a cause of higher prices, and we shall deal with the doctrine again, in a different connection. By devitalizing the marginal utility theory, by stating it in such a way that it makes no causal assertions, and in such a way that it leaves the real value problem untouched, it is possible to free it from the circle just pointed out. Schumpeter does so state it.