view. To maintain that Economy must stop short at this or that degree of abstraction, and for example be limited to what are called external goods or riches, excluding services; or to capital, as a concept distinct from land and human labour, without striving to unify these three concepts, is altogether capricious. Every unification, like every specification, can be useful, and haters of abstracticism are also abstracticists, but only half so. [Sidenote: _dance at the History of the various tendencies of Economy._] All those acquainted with economic studies will have recognized in the concepts that we have explained, the _logical motives_ of the history of Economy, the divisions, the polemics, the defeats and the victories of this or that school and the progress of that branch of studies. The quantitative character of economic science already appears in its classics; in the inquiries of Aristotle as to prices and value (_Politic_ and _Nichomachean Ethic_); and this is apparent also in the rare mentions by Mediæval and Renaissance writers. Economists have always been mathematicians, even when they have not spoken of mathematical Economy. Our writers of the nineteenth century, Galiani, Genovesi and Verri, were mathematicians in their methods; Francesco Ferrara, the greatest Italian economist of the nineteenth century, was a mathematician. The economic principle, which is all one with the excogitation of the economic man, was formulated by the head of the physiocratic school, Quesnay; and if the title of _political Economy,_ first given to the discipline by Montchrétien in 1615, prevailed, that of _social Arithmetic_ also sometimes made its appearance. Its progress has consisted, not only in the discovery of new economic theorems, but also in the connection and unification of those that had previously been posited in isolation, of material and immaterial goods, of the cost of production and of rarity, of gross and net produce, of agricultural rents and of all the others that are not agricultural, of the production, distribution and circulation of riches, of economic and financial laws, of social and isolated economy, of the value of utility and of the value of exchange. It has even been possible to unite with the body of admitted economic doctrines those of Marx, which seemed revolutionary, for these are only definitions of a particular casuistry founded upon the comparison of different types of economic constitution.