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 published his "Principles of Political Economy" in the year 1817. Ricardo's great service consisted in pointing out that wealth, whether in the form of capital or otherwise, is merely the accumulated product of labor, and in enforcing Adam Smith's position that labor is the sole basis of value, with its corollary that the "natural price" of a commodity expresses the total amount of embodied social labor it contains. We should also mention that he was the first to definitely formulate the theory of "economic rent," by which is meant the surplus yield or produce from any land over and above that of the worst land in cultivation.

Adam Smith, Malthus, and Ricardo constitute the trinity of the classical economy. The doctrines laid down by them were expanded, illustrated and popularized by a series of writers whom the Germans have named epigoni, and who consisted of James Mill, McCulloch, Senior, and others.

Before saying a few words on what is called the "vulgar" economy, we must not forget to mention John Stuart Mill (1806-1873), who, although in no sense an original thinker, is one of the most popular writers on political economy. His "Principles of Political Economy," published in 1848, though in substance little more than a manual of the classical system, is distinguished by breadth of sympathy, and by the consciousness that the so-called economic laws, that is, the deductions of political economy based on the present conditions of society, have not the absolute character other exponents of the science were apt to assign to them. At the same time it must be remembered that J. S. Mill was totally deficient in what has been sometimes called the "historical sense" and had little conception of the historical method. His heart rebelled against the