The word «exchange» has continued to be employed after having quitted the system of barter to enter upon the system of buying and selling, by means of money, just as the expression «money» has continued to be used to describe bank-notes, which are only paper having the power of money, as money is an instrument having the power of «things.» Thus we have here an example of the general rule, that the evolution of ideas and of facts, is always more rapid than that of the words which represent them. Our opinion with regard to «exchange» will be found all the more justified since it will be seen later on that the power conferred by money upon the seller does not exclusively belong to the monetary system, but that it can be obtained, and that theoretically it always could be obtained, in quite another way, without exchanging anything, without having anything to do with money, by simple entry, registering or writing down of figures on paper which is not exchanged, but which remains in one's own hands. Let us now come back to the question. We proceed to show that the relative value of things is independent of the unity of value chosen, and that the transactions can be registered, written down, abstraction made of the real, actual value of the material support which has served to fix this unity. In a general way and within possibly narrow limits, very different and variable according as the case may be, given the existence in actual society of fortunes and desires of all degrees of importance, one can, in principle, admit that theoretically, the value _v_ of a thing or of a certain quantity of goods, is proportional to the average _d_ of the desire to possess it, which the men demanding it have, either on account of its use, or from any other reason, multiplied by the number _h_ of these men and divided by the number _o_ offered of this thing; these three factors _d_, _h_ and _o_ not being probably in other respects determinable with precision. We shall then have for the formula of value: _v_ = _u_ × _dh/o_ _u_ being a coefficient of proportionality depending on the unity of value adopted. It will be seen that the term _dh/o_ represents in reality the account of the conditions of the supply and of the demand at the moment and at the place where the value is determined[B]. In substituting E, we have a new term expressive of the value: _v_ = _u_ × E.