In that relationship, the copper is only considered as a body that represents weight. Thus dispenses with its other properties and serves only as a measure of weight. Similarly, expressing any value for example, fifteen metres of linen are worth a costume – the second merchandise only represents value. The particular usefulness of the suit is not taken into account in this case and only serves as a measure of value of the linen. But there ends the similarity. In the expression of the weight of the lump of salt, copper represents a quality common to both bodies, but is a natural quality: his weight. In the value expression of the linen with the costume, this staring represents a quality common to the two objects, but it is no longer a natural quality but of social origin: its value.

Merchandise that has a double aspect – object of utility and value – does not appear as it is, but when you stop to consider it in isolation, when by its relationship with other merchandise, the possibility of being changed, acquires its value a measurably: from change, other than its natural form value. Not the goods go by themselves to the market or changed between them, to put them in touch its possessors, have to be set at the same time, mutual relations, so that each who appropriates merchandise self-employed person delivering their own, through a common voluntary act. This legal relationship is the contract whereby two people there as representatives of the goods. FORM of value: Concept of values, all goods are expressive of human work unit – and they can replace each other. Therefore, a commodity can change for other merchandise. In fact there are impossibility of immediate change between the goods. One of them takes the suitable form of immediate change, with all the others. Well known is that the goods have a special form of value: how currency, which has its foundation in the simple form of the gear ratio.