Malthus had already produced a book on the subject,[317] and Ricardo hails him as the discoverer of the true doctrine of rent. Malthus takes as his starting-point the explanation offered by the Physiocrats and Adam Smith, namely, that rent is the natural outcome of some special feature possessed by the earth and given it by God—that is, the power of enabling more people to live on it than are required to till it. Rent is the result, not of a merely physical law, but also of an economic one, for nature seems to have a unique power of creating a demand for its products, and consequently of maintaining and even of increasing indefinitely both its own revenue and value. The reason for this is that the population always tends to equal and sometimes to surpass the means of subsistence. In other words, the number of people born is seldom less than the maximum number that the earth can feed. This new theory of rent is a simple deduction from Malthus’s law concerning the constant pressure of population upon the means of subsistence. Malthus emphasised another important feature of rent, and it was this characteristic that especially attracted Ricardo. Seeing that different parts of the earth are of unequal fertility, the capitals employed in cultivation must of necessity yield unequal profits. The difference between the normal rate of profit on mediocre lands and the superior rate yielded by the more fertile land constitutes a special kind of profit which is immediately seized by the owner of the more fertile land. This extra profit afterwards became known as differential rent. To Malthus, as well as to the Physiocrats, this kind of rent seemed perfectly legitimate and conformed to the best interests of the public. It was only the just recompense for the “strength and talent” exercised by the original proprietors. The same argument applies to those who have since bought the land, for it must have been bought with the “fruits of industry and talent.” Its benefits are permanent and independent of the proprietor’s labour, and in this way the possession of land becomes a much-coveted prize, the _otium cum dignitate_ which is the just reward of meritorious effort. Ricardo enters upon an entirely new track. He breaks the connection with Smith and the Physiocrats—a connection that Malthus had been most anxious to maintain. All suggestion of co-operation on the part of nature is brushed aside with contempt. Business-man and owner of property as he was, he had no superstitious views concerning nature, whose work he contemplated without much feeling of reverence. As against the celebrated phrase of Adam Smith he quotes that of Buchanan: “The notion of agriculture yielding a produce and a rent in consequence because nature concurs with human industry in the process of cultivation is a mere fancy.”[318] He proceeds to defend the converse of Smith’s view and to show how rent implies the avarice rather than the liberality of nature.