The germs of the _Ricardo_ law of rent, in _Boisguillebert_: the price of corn determines how far the cultivation may be extended; by manuring the land, as much corn as desired may be obtained, provided the cost of production is covered. (Traité des Grains, II, ch. 2 ff.) There is a foreshowing of the same law in the Physiocratic view that only in the production of raw material is there a real excess over and above the cost--_produit net_. Compare _Quesnay_, Probl., économique, 177 ff. Sur les travaux des artisans. (Daire.) _Auxiron_, Principes de tout Gouvernement, 1776, I, 126. _Adam Smith_ came very near to the true principle in the case of coal mines, but was hindered reaching it in other cases by the false assumption that certain kinds of agricultural production always yield a rent, while others do so only under certain circumstances. Besides he always considered the interest of capital fixed in the soil; buildings, for instance, as part of the rent. (Wealth of Nat., I, ch. 11.) Compare _Hume's_ Letter to Adam Smith; _Burton's_ Life and Correspondence of Hume, II, 486; _von Thünen_, Isolirter Staat., I, 15 ff. The most immediate predecessors of _Ricardo_, Principles, 2, 3, 24, 31, are _Anderson_ (§ 152); _West_, Essay on the Application of Capital to Land, 1815, and _Malthus_, Inquiry into the Nature and Progress of Rent, 1815. See § 152. It is wonderful how a theory which, in 1777, remained almost untouched, was in 1815 etc., attacked and defended with the greatest zeal, because it then affected the differences between the moneyed and landed interest. Yet _Ricardo_ did not take into account at all the rent-creating influence of the situation of land in relation to the market, as well as to the "farm-office" (_dem Wirthschaftshofe_). The influence of the system of husbandry on rent, first thoroughly treated by _von Thünen_, loc. cit. What has recently been urged against _Ricardo_ by, for instance, _J. B. Say_, Traité, II, ch. 9; _Sismondi_, N. P., III, ch. 12; _Jones_, Essay on the Distribution of Wealth, 1831 (see Edinburg Review, LIV), bears evidence either of a misunderstanding of the great thinker, or else contains only modifications of some individual abstract propositions of his, stated perhaps too strictly. In judging _Ricardo_, it must not be forgotten, that it was not his intention to write a text-book on the science of Political Economy, but only to communicate to those versed in it the result of his researches, in as brief a manner as possible. Hence he writes so frequently making certain assumptions; and his words are to be extended to other cases only after due consideration, or rather re-written to suit the changed case.