Another misconception exists on the subject of gold, or rather of money. As it is the constant medium which enters into all transactions, the mean term between the two factors of ‹compound barter›, it is always with its value that we compare the value of the two services to be exchanged; and hence we are led to regard gold or money as a ‹measure› of value. In practice it cannot be otherwise. But science ought never to forget that money, so far as its value is concerned, is subject to the same fluctuations as any other product or service. Science does forget this sometimes; nor is it surprising. Everything tends to make us consider money [p152] as the measure of value, in the same way as the ‹litre› (or quart) is the measure of capacity. It plays an analogous part in actual business. One is not aware of its own fluctuations, because the franc, like its multiples and sub-multiples, always retains the same denomination. And arithmetic itself tends to propagate the confusion by ranking the franc as a measure, along with the measures of quantity in daily use. I have given a definition of Value, at least of value according to my idea of it. I have subjected that definition to the test of divers facts. None of them, so far as I can see, contradict it; and the scientific signification which I have given to the word agrees with its vulgar acceptation, which is no small advantage, no slight guarantee—for what is science but experience classified? What is theory but the methodical exposition of universal practice? I may now be permitted to glance rapidly at the systems which have hitherto prevailed. It is not in a spirit of controversy, much less of criticism, that I enter upon this examination, and I should willingly avoid it were I not convinced that it will throw new light upon the fundamental principles which I am advocating. We have seen that writers on Political Economy have sought for the principle of Value in one or more of the accidents which exercise a notable influence over it, such as materiality, conservability, utility, rarity, labour, etc.; just like a physiologist who should seek the principle of life in one or more of the external phenomena which are necessary to its development, as air, water, light, electricity, etc. ‹Materiality.›—“Man,” says M. de Bonald, “is mind served by organs.” If the economists of the materialist school had simply meant that men can render reciprocal services to each other only through the medium of their bodily organs, and had thence concluded that there is always something material in these services, and, consequently, in Value, I should not have proceeded a step farther, as I have a horror at word-catching and subtilties, which wit revels in.