Section XXII. Former Methods. The methods(159) which would apply to any science of national life, principles borrowed from any other science, are now generally looked upon as obsolete. This is true, especially, of the theological method which prevailed, almost exclusively during the middle ages,(160) and of the juridical method of the seventeenth century. It would be much more in harmony with the intellectual tendencies of the time, to adopt a mathematical mode of treatment in Political Economy, involving, as such a mode of treatment does, not the matter of the science, but only a formal principle. That which is general in Political Economy has, it must be acknowledged, much that is analogous to the mathematical sciences. Like the latter, it swarms with abstractions.(161) Just as there are, strictly speaking, no mathematical lines or points in nature, and no mathematical lever, there is nowhere such a thing as production or rent, entirely pure and simple. The mathematical laws of motion operate in a hypothetical vacuum, and, where applied, are subjected to important modifications, in consequence of atmospheric resistance. Something similar is true of most of the laws of our science; as, for instance, those in accordance with which the price of commodities is fixed by the buyer and seller. It also, always supposes the parties to the contract to be guided only by a sense of their own best interest, and not to be influenced by secondary considerations. It is not, therefore, to be wondered at, that many authors have endeavored to clothe the laws of Political Economy in algebraic formulæ.(162) And, indeed, wherever magnitudes and the relations of magnitudes to one another are treated of, it must be possible to subject them to calculation. Herbart has shown that this is so in the case of psychology;(163) and all the sciences which treat of national life, especially our own, are psychological.(164) But the advantages of the mathematical mode of expression diminish as the facts to which it is applied become more complicated. This is true even in the ordinary psychology of the individual. How much more, therefore, in the portraying of national life! Here the algebraic formulæ would soon become so complicated, as to make all further progress in the operation next to impossible.(165) Their employment, especially in a science whose sphere it is, at present, to increase the number of the facts observed, to make them the object of exhaustive investigation, and vary the combinations into which they may be made to enter, is a matter of great difficulty, if not entirely impossible.(166) For, most assuredly, as our science has to do with men, it must take them and treat them as they actually are, moved at once by very different and non-economic motives, belonging to an entirely definite people, state, age etc. The abstraction according to which all men are by nature the same, different only in