In the study of economic categories, as in the case of every historical and social science, it must be borne in mind that as in reality so in our mind the subject, in this case modern bourgeois society, is given and that the categories are therefore but forms of expression, manifestations of existence, and frequently but one-sided aspects of this subject, this definite society; and that, therefore, the origin of [political economy] as a science does not by any means date from the time to which it is referred as such. This is to be firmly held in mind because it has an immediate and important bearing on the matter of the subdivisions of the science.
For instance, nothing seems more natural than to start with rent, with landed property, since it is bound up with land, the source of all production and all existence, and with the first form of production in all more or less settled communities, viz. agriculture. But nothing would be more erroneous. Under all forms of society there is a certain industry which predominates over all the rest and whose condition therefore determines the rank and influence of all the rest.
It is the universal light with which all the other colors are tinged and are modified through