The theory of value, as I conceive it, is, then, not a substitute for detailed price analysis, but rather a presupposition of it. The theory of value is to interpret, validate, and guide the theory of prices. If the theory here outlined be true, it will have significant consequences for the theory of prices, in that it will open up new problems for the price analysis to attack. There are many social forces which can be measured with substantial accuracy, and many more which can be, for purposes of theory, disentangled from the complex in which they appear, and treated by the methods of price analysis already discussed, which economic theory has not yet thought it worth while to attack. The economist must emulate the practical business man, in trying to treat in price terms the various social changes which affect economic values. There is much left for the theory of prices to do. The theory defended here, with its sharp sundering of values and prices, will, of course, criticize the mixing of the two. One chief criticism of the Austrian theory, and also of the theory of the English School in so far as it attempts to give a "real cost" doctrine, is that they are attempts to give both a theory of value and a theory of prices at the same time. Certainly we must object to Boehm-Bawerk's contention that the solving of the price problem _ipso facto_ solves the value problem.[214] The purpose of this book is, not _destructive_, but _reconstructive_. A detailed criticism of the various economic theories that have appeared, as theories of prices, is manifestly too big a task to be undertaken here. All of them cannot, of course, be accepted _in toto_, for there are, doubtless, irreconcilable differences among them at points. But it is the belief of the writer that the great bulk of what has been done in the study of the quasi-mathematical laws of prices is of substantial worth, that a recognition of the distinction between value theory and price theory, and of the confusions that result from mixing the two, will remove many seemingly irreconcilable differences between opposing schools, and that existing price theories are less to be criticized for what they affirm than for what they ignore and deny. Much of the significance of the theory of value for the interpretation of price theory has been indicated from time to time, in what has gone before. Prices have _meanings_. They express _values_. To understand the meanings of prices, we must know what the values mean. There is one further point in this connection which is so important that we shall give a separate chapter to it. FOOTNOTES: [210] _Vide supra_, chaps. V and XI. [211] _Natural Value_, _passim_.