If we compare, with regard to method, Adam Smith's Wealth of Nations with Karl Marx's Capital, the decisive and also most obvious difference is this: while the former is an attempt to generalize from experience (as found in historical and statistical records, but also in conversations with Glasgow merchants) and to check those generalizations by trying to explain an ever wider range of empirical phenomena (according to the canons of Newtonian science), the latter is — as the subtitle indicates — a Critique of Political Economy which starts from the theoretical presuppositions of bourgeois economists in order to show how their categories and laws partly reveal and partly hide, but are essentially unable to explain, the reality of the capitalist economic system. For Smith, the reading of earlier and contemporary economic treatises served to clarify his own views, but he had no need of mercantilist or physiocratic ideas in order to explain his own theory. When rather late in his work (in Book IV) he discusses those ideas, it is only to show the superiority of his own system. Marx, on the contrary, carefully studied two hundred years of economic literature in order to discover the "anatomy of bourgeois society" and introduces as premises of his critical theory (at the beginning of Book I) what he takes to be the basic categories and principles of "classical political economy".