There is no disagreement, then, between the Philosophy of Economy described by us and economic Science or Calculus, of which we have just defined the nature, since there cannot be any between two altogether heterogeneous forms, the one moving within the categories of truth, the other outside them, with objects of a practical order. This reciprocal tolerance can be disturbed only by Philosophy, when it compels itself, either to invade the field of economic Science, or to receive within itself, to a greater or less extent, the method and the formulæ proper to the latter. We have already referred to the first, when we noted the inadmissibility of the economic attempts of philosophism and historicism, and we will say no more on the subject. But it is opportune to draw attention to the fact that we must distinguish among these attempts those that we are accustomed to meet with in many treatises on economy, pure or political, and in the Science of finance (especially in the prologues), which labour to discover what economic action may be, and in what way it differs from morality, what are pleasure and pain, utility and value; whether the State be rational will that levies a portion of the riches of the citizens for the ends of civilization, or a simple fact resulting from general economic laws and the like. In all these efforts of the writers of treatises, we have an example of the gradual passage from empiria to philosophy, which is to be observed in all the other fields of knowledge, and if it be only possible to say in general that the Philosophy of Economy is derived from economic Science, it is certain, on the other hand, that it finds no small incentive in the philosophical doubts and discussions which economic Science supports. On the other hand, the claim to resolve philosophically and historically the economic Science or Calculus is, as we have seen, altogether sterile, or contradicts itself in development. [Sidenote: _Errors that derive from it._] From the second of the cases stated above, that is to say, from the mixture of economic with philosophic methods, arises a series of errors that are very common and very grave, and of which it is opportune to take some notice here. These errors can be divided into three groups, according as they consist of _(a)_ considering economic Science or Calculus as a method exclusive of every other, and alone capable of bestowing upon man all the truth that can ever be attained in the field of human actions; _(b)_ in attributing the value of universal thought to the empirical thoughts upon which economic calculation is based; _(c)_ in changing into reality the fictions excogitated for the establishment of the Calculus. [Sidenote: _1st. Negation of philosophy for economy._]