Thus far we have considered differential rent only as the result of varying productivity of equal amounts of capital invested in equal areas of land of different fertility, so that differential rent was determined by the difference between the yield from the capital invested in the worst, rentless soil and that from the capital invested in superior soil. We had side by side capitals invested in different plots of land, so that every new investment of capital signified a more extensive cultivation of the soil, an expansion of cultivated area. In the last analysis, however, differential rent was by its nature merely the result of the different productivity of equal capitals invested in land.
In the study of differential rent II, the following points are still to be emphasized.
First, its basis and point of departure, not just historically, but also in so far as concerns its movements at any given period of time, is differential rent I, that is, the simultaneous cultivation side by side of soils of unequal fertility and location; in other words, the simultaneous application, side by side, of unequal portions of the total agricultural capital upon plots of land of unequal quality.
It should therefore be remembered from the outset that differential rent I is the historical basis which serves as a point of departure. On the other hand, the movement of differential rent II at any given moment occurs only within a sphere which is itself but the variegated basis of differential rent I.
Secondly, in the differential rent in form II, the differences in distribution of capital (and ability to obtain credit) among tenants are added to the differences in fertility. In manufacturing proper, each line of business rapidly develops its own minimum volume of business and a corresponding minimum of capital, below which no individual business can be conducted successfully. In the same way, each line of business develops a normal average amount of capital above this minimum, which the bulk of producers should, and do, command. A larger volume of capital can produce extra profit; a smaller volume does not so much as yield the average profit.
It is true that the peasant, for example, expends much labour on his small plot of land. But it is labour isolated from objective social and material conditions of productivity, labour robbed and stripped of these conditions.
Let us first consider just the formation of surplus-profit with differential rent II, without for the present bothering about the conditions under which the transformation of this surplus-profit into ground-rent may take place.
It is then evident that differential rent II is merely differently expressed differential rent I, but identical to it in substance. The variation in fertility of various soil types exerts its influence in the case of differential rent I only in so far as unequal results are attained by capitals invested in the soil, i.e., the amount of products obtained either with respect to equal magnitudes of capital, or proportionate amounts. Whether this inequality takes place for various capitals invested successively in the same land or for capitals invested in several plots of differing soil type — this can change nothing in the difference in fertility nor in its product and can therefore change nothing in the formation of differential rent for the more productively invested portions of capital. It is still the soil which, now as before, shows different fertility with the same investment of capital, save that here the same soil performs for a capital successively invested in different portions what various kinds of soil do in the case of differential rent I for different equal portions of social capital invested in them.
