population. It is already impossible to take J.S. Mill's _Principles of Political Economy_ as a text-book. Important as it was for thirty or forty years, it will soon be as little read as M'Culloch's _Principles_. For the rest of the economists of this period, it is difficult to see how they can escape oblivion. When the generation whose economic training was based upon J.S. Mill has died out, the relevance of the "old Political Economy" is not likely to be a question of any interest to ordinary educated men and women, or even to the great mass of economic students. The explanation of this decay of interest does not lie upon the surface. It is frequently supposed that the influence of the "old Political Economy" has been gradually undermined by the attacks of the historical school. But great as the achievements of this school have been, it has not developed any scientific machinery which can take the place of theory in economic investigation. If our view is correct that, broadly speaking, the two ways of regarding economic questions are complementary rather than mutually exclusive, there does not seem to be any reason why the growth of the historical school should have been destructive of the "old Political Economy" if it had been well founded. The use of the historical method has, in fact, raised more reputations than it has destroyed, because by keeping carefully in view the conditions in which economic works have been written, it has shown that many theories hastily condemned as unsound by _a priori_ critics had much to be said for them at the time when they were propounded. This observation is true not only of old-world writers like the Mercantilists, but also of Ricardian economics. No one is concerned to prove that the Ricardian economics applies to the manorial system, and it is generally supposed at any rate that the world has been approximating more and more nearly during the last century to the conditions assumed in most of the reasoning of that school. On the principles we have explained, therefore, the Ricardian economics should supply just that body of general theory which is required in the investigation of modern economic problems, and the reputation of at any rate the leading writers should be as great as ever. It would be of immense advantage from a scientific point of view if this could be taken for granted, if for a time the work of the classical economists could be considered final so far as it goes, and for the purposes of investigation regarded as the theoretical counterpart of the modern industrial system. This assumption, however, has been made quite impossible, not by the historical school, but by the criticism and analysis of economists in the direct line of the Ricardian succession. Ricardo's limitations.