"Political economy begins with commodities, with the moment when products are exchanged, either by individuals or by primitive communities. The product being exchanged is a commodity. But it is a commodity merely by virtue of the thing, the product being linked with a relation between two persons or communities, the relation between producer and consumer, who at this stage are no longer united in the same person. Here is at once an example of a peculiar fact, which pervades the whole economy and has produced serious confusion in the minds of bourgeois economists — economics is not concerned with things but with relations between persons, and in the final analysis between classes; these relations however are always bound to things and appear as things''.

Engels