We must clarify in our minds wherein lies the real difficulty in analysing ground-rent from the viewpoint of modern economics, as the theoretical expression of the capitalist mode of production. Even many of the more modern writers have not as yet grasped this, as evidenced by each renewed attempt to "newly" explain ground-rent. The novelty almost invariably consists in a relapse into long out-of-date views. The difficulty is not to explain the surplus-product produced by agricultural capital and its corresponding surplus-value in general. This question is solved in the analysis of the surplus-value produced by all productive capital, in whatever sphere it may be invested. The difficulty consists rather in showing the source of the excess of surplus-value paid the landlord by capital invested in land in the form of rent, after equalisation of the surplus-value to the average profit among the various capitals, after the various capitals have shared in the total surplus-value produced by the social capital in all spheres of production in proportion to their relative size; in other words, the source subsequent to this equalisation and the apparently already completed distribution of all surplus-value which, in general, is to be distributed. Quite apart from the practical motives, which prodded modern economists as spokesmen of industrial capital against landed property to investigate this question — motives which we shall point out more clearly in the chapter on history of ground-rent — the question was of paramount interest to them as theorists. To admit that the appearance of rent for capital invested in agriculture is due to some particular effect produced by the sphere of investment itself, due to singular qualities of the earth’s crust itself, is tantamount to giving up the conception of value as such, thus tantamount to abandoning all attempts at a scientific understanding of this field. Even the simple observation that rent is paid out of the price of agricultural produce — which takes place even where rent is paid in kind if the farmer is to recover his price of production — showed the absurdity of attempting to explain the excess of this price over the ordinary price of production; in other words, to explain the relative dearness of agricultural products on the basis of the excess of natural productivity of agricultural production over the productivity of other lines of production. For the reverse is true: the more productive labour is, the cheaper is every aliquot part of its product, because so much greater is the mass of use-values incorporating the same quantity of labour, i.e., the same value.