Smith opens his treatment by emphasising the fundamental distinction which exists between “value in use” and “value in exchange.”[171] By value in use he means almost[172] exactly what we understand by utility, or what other writers call subjective value, desirability, or ophelimity. Present-day economists when treating of prices—the exchange value of things—chiefly rely upon this conception of “value in use.” The explanation of the “ratio of exchange” of commodities is based upon a previous analysis of their utility for those who exchange them. Smith proceeds in a different fashion. “Value in use” is mentioned, but only for the purpose of contrasting it with value in exchange. It is then dismissed without further consideration. The two notions seem to have no point of contact. Value in exchange was the only one that was of any interest to Smith; hence there was all the more reason for denying its derivative character.[173] Thus from the very first the only avenue that might have led to a satisfactory solution of this problem of prices was closed. One could easily have predicted that this was bound to land Smith in difficulty; as a matter of fact he is doubly involved.[174] Two different but equally erroneous solutions have been successively adopted by him, but he has never actually decided between them. The socialists and economists who are to follow will be engaged in the same task, and the cleavage between them will be marked by their adoption of one or other of these two theories. Smith was led to the study of prices because he wished to know something of the constant oscillation which is such a feature of their history. The actual or market price is unstable because of the unstable connection between demand and supply,[175] or, as he puts it, “It is adjusted, however, not by any accurate measure, but by the higgling and bargaining of the market, according to that sort of rough equality which, though not exact, is sufficient for carrying on the business of common life.”[176] It seemed impossible that their perpetual fluctuation should represent the true value of the commodity. Its real value could not vary from this moment to the next or from one place to another. Underneath the constantly oscillating market price may be discerned another price, referred to by Smith as the real or sometimes as the natural price. The discovery of a more stable and a more constant element beneath the continual fluctuations of price movements still constitutes the great problem of pure economics.[177]