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 its peculiarity. It is a special ether which determines the specific gravity of everything that appears in it. Let us take for example pastoral nations (mere hunting and fishing tribes are not as yet at the point from which real development commences). They engage in a certain form of agriculture, sporadically. The nature of land-ownership is determined thereby. It is held in common and retains this form more or less according to the extent to which these nations hold on to traditions; such e. g. is land-ownership among the Slavs. Among nations whose agriculture is carried on by a settled population―the settled state constituting a great advance―where agriculture is the predominant industry, such as in ancient and feudal societies, even the manufacturing industry and its organization, as well as the forms of property which pertain to it, have more or less the characteristic features of the prevailing system of land ownership; [society] is then either entirely dependent upon agriculture, as in the case of ancient Rome, or, as in the middle ages, it imitates in its city relations the forms of organization prevailing in the country. Even capital, with the exception of pure money capital, has, in the form of the traditional working tool, the characteristics of land ownership in the Middle Ages.