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OF THE SOLUTION OF AN ECONOMIC PROBLEM, AND OF
THE DEGREE OF PERFECTION OF WHICH IT IS SUSCEP
In treating in my last lecture of the method of inquiry proper to Political Economy, I was led to an examination of the nature of the assertion contained in an economic law, and the kind of proof that was required for establishing or refuting it. On these points I arrived at the following conclusions, viz. that an economic law expresses, not the order in which phenomena occur, but a tendency which they obey ; that, therefore, when applied to external events, it is true only in the absence of disturbing causes, and consequently represents a hypothetical, not a positive truth; that, being deduced by necessary consequence from certain mental and physical principles, it can be established only by establishing the existence of the principles assumed, and showing that by logical necessity they involve the tendency asserted ; and refuted only by proving that the principles do not exist, or that the reasoning is unsound. In all these respects I endeavoured to show that the character of an economic law is strictly analogous to that of those laws of physical nature which are obtained, or which
may be obtained, by deduction from the ultimate principles of the sciences to which they belong.
In alluding, however, to the nature of the proof by which the ultimate premises of Political Economy are established, as compared with the process by which ultimate physical truths are obtained, you will probably remember that I noticed a difference between Political Economy and the physical sciences in this respect ; the ultimate truths on which the existing structure of physical science is based, having been arrived at through a series of inductive steps, proceeding upwards from the empiric generalization of physical phenomena, to the ultimate laws of force and motion on which they depend; while for the ultimate truths of economic science we are independent of this inductive process, having the direct proof afforded by our own senses and consciousness. The advantage, however, which Political Economy enjoys in this respect over physical science, is perhaps more than compensated by a disadvantage under which it labours in another, which affects very materially the degree of perfection to which it can be brought; and to this circumstance and the consequences which result from it I proceed now to call attention.
In the more advanced physical sciences, as I have already more than once remarked, a law of nature expresses some general tendency constantly influencing external objects; and in this respect it is precisely similar to a law in Political Economy; but in the physical sciences the discovery of a law of nature is never considered complete till, in addition to the general ; tendency, an exact numerical expression be found for the degree of force with which the tendency in question operates. “It is the character,” says Sir John Herschel,* “ of all the higher laws of nature to assume the form of precise quantitative statement. Thus the law of gravitation, the most universal truth at which human reason has yet arrived, expresses not merely the general fact of the mutual attraction of all matter; not merely the vague statement that the influence decreases as the distance increases, but the exact numerical rate at which that decrease takes place ; so that, when its amount is known at any one distance, it may be calculated exactly for any other. Thus, too, the laws of crystallography, which limit the forms assumed by natural substances, when left to their own adherent powers of aggregation, to precise geometrical figures with fixed angles and proportions, have the same essential character of strict mathematical expression, without which no exact particular conclusions could ever be drawn from them.” To give one example more, the use of the balance has brought chemistry into the category of those sciences the laws of which admit of quantitative statement. The chemist is consequently able, not merely to describe the general nature of the reaction which will take place between certain substances under known conditions, but can give beforehand a numerical state
ment of the exact proportions in which the several elements will unite in the resulting compound.
This is a degree of perfection, however, which it does not seem possible that Political Economy should ever attain. A portion of the premises of this science, and that portion which comes most constantly into play in all economic reasonings, consists, as you are aware, of those principles of human nature which influence mankind in the pursuit of wealth. Now, although the general character of these principles may be ascertained, and when stated with sufficient precision may be made the basis of important deductions, yet such principles do not, from their nature, admit of being weighed and measured like the elements and forces of the material world ; they are therefore not susceptible of arithmetical or mathematical expression ; and hence it happens that, in speculating on results which depend on the positive or relative strength of such principles, perfect precision and certainty are not attainable. Political Economy seems on this account necessarily excluded from the domain of exact science.*
* Mr. Macleod considers Monetary Science, (which he appears to regard as commensurate or nearly so with Political Economy) as “an exact science.” In the Introduction to his “ Theory and Practice of Banking,” vol. 2, p. 25, he writes as follows :-“These principles then act with unerring certainty—they are universally true-human instinct is as certain, invariable, and universal in its nature as the laws of motion—AND THAT IS THE CIRCUMSTANCE WHICH RAISES MONETARY SCIENCE TO THE RANK OF AN EXACT OR INDUCTIVE SCIENCE. It is this which renders it possible to establish it upon as sure, solid, and unimperishable a basis as mechanical science. Alone of all the
This quality of economic doctrines will be made more clear by a few examples.
political sciences its phenomena may be expressed with the unerring certainty of the other laws of nature.” Mr. Macleod seems to confound an “exact” with a positive science. In order that a science be “ exact,” it is necessary, not only that its premises be “universal and invariable,” but further, that they be susceptible of precise quantitative statement. If Mr. Macleod can show not only that the character of “human instinct" can be known, but also that its force can be measured, as the force of gravitation, he will then have established a basis for an exact science of Political Economy.
Mr. Jennings, in his “Natural Elements of Political Economy,” appears to take the same view. “Our instruments,” he says, “though acting on and through the principles of human nature, are found to consist of metallic indices (money] related as parts and multiples, and not less capable of being made subservient to the processes of exact calculation than are the instruments of any purely physical act. The results of these principles when observed may be expressed in figures ; as may also the anticipated results of their future operation, or such relations as those of Quantity and Value, Value and Rate of Production may be exhibited in the formulæ and analyzed by the different methods of Algebra and of Fluxions.”—pp. 259–260.
There is no doubt that economic results, when they have happened, may be expressed in figures ; but I apprehend something more than this is requisite to render a science "exact.” Mr. Jennings indeed adds, "as may also the anticipated results of their future operation ;" but the question is, have we such data as will render reliable the results thus obtained ? Will our calculations turn out not merely generally, but “exactly” true ? Instead of dealing in general terms, let us take a specific case—the determination of the price of corn, and consider what in this instance would be necessary in order to arrive at an “exact” result. The following is taken from Tooke's History of Prices :-“But, further,--supposing that both the results of the harvests and the stock on hand were made known with sufficient approach to accuracy by Government returns, there would yet remain the greatest uncertainty in the corn markets unless the probable extent of the Supplies from abroad could be known. And, granting all these grounds for estimates of actual and forthcoming supplies to be within the power of Government to ascertain, there would be yet another