_Second case._ Let the labor-time required for the production of commodity A remain constant. Then the exchange value of A, expressed in terms of B, falls and rises in an inverse ratio with the rise and fall of the labor-time required for the production of B. _Third case._ Let the labor-time required for the production of commodities A and B rise and fall in equal proportion. Then the expression of equivalence of A and B remains unchanged. If through some cause the productivity of all kinds of labor were to decline uniformly, so that the production of all commodities would require an equally increased quantity of labor-time, then the value of all commodities would rise, though the expression of their exchange values would remain unchanged, and the actual wealth of society would decrease, because it would have to expend more labor-time on the production of the same stock of use-values. _Fourth case._ Let the labor-time required for the production of A and B rise and fall, but not uniformly; that is to say, the labor-time required for the production of A may rise, while that required for B may fall, or vice versa. All of which can be reduced to the simple case where the labor-time required for the production of one commodity remains unchanged, while that required for the other rises or falls. The exchange value of any commodity is expressed in the use-value of any other commodity, be it in integral units or in fractions thereof. As exchange value, every commodity is capable of subdivision, like the labor-time embodied in it. The equivalence of commodities is independent of their physical divisibility as use-values, just as the sum of the exchange values of commodities is indifferent to the change of form which use-values have to undergo when converted into a _single_ new commodity. So far we have considered commodities from a twofold point of view, as use-values and exchange values alternately. But a commodity as such is a direct combination of use-value and exchange value; and it is a commodity only in relation to other commodities. The _actual_ relation between commodities constitutes the _process of their exchange_. It is a social process participated in by individuals independent of each other but the part they take in it is that of owners of commodities only. Their mutual relations are those of their commodities, and thus they really appear as conscious factors of the process of exchange.