In the beginning the relative quantities of the products exchanged for each other must have varied greatly. But in course of time the exchange of commodities took place in a ratio fixed for any one place and time; ten hatchets, for example, being equivalent to five bows, etc. These commodities must have a common quality which makes a comparison possible; and it is this common quality which we call their value. The first problem to be solved, then, is this: “What constitutes the value of commodities?” To become a commodity anything must provide for some need of man; it must have the value of usefulness. Without this value a product can never be a commodity. However, it is impossible that the quality which different commodities have in common, and on the basis of which they are compared, should be their usefulness, that is to say, their natural qualities. For it is just because of their difference in usefulness [to their possessors] that goods are exchanged. “As regards their use-value goods are primarily of different quality; as regards their exchange-value they can only be of different quantity, without including a particle of use-value.” [268] Since usefulness does not count in exchange there is only one quality of the commodity that remains, that of being the product of labor. And as we have withdrawn the consideration of usefulness in estimating exchange-value, we must do the same for different kinds of work, so that the only quality which remains to a commodity is that of being the product of the labor of man in general. Any commodity, then, derives its value only from the circumstance that it represents a certain amount of labor of man in general. The value of a commodity is determined by the quantity of labor it represents, measured by the time required. Naturally by “work” is to be understood here not individual work, but social work; or as Marx says: “It is ... the quantity of work socially necessary, or the time socially necessary for the production of a commodity, which determines its value.” [269] In measure as the division of labor is developed, production for personal use diminishes, and the production of commodities increases, until it finally becomes the universal form of production, and one commodity (money) is developed as a universal equivalent. As a consequence of the development of the production of merchandise, the purchase and sale of goods becomes a special profession. The merchant buys for a different reason from that which influences his customers. While the latter buy for consumption, the former buys to sell again and make a profit out of the transaction. The commodity which serves for this purpose is called capital.