Essays on some unsettled Questions of Political Economy

by John Stuart Mill

This ought not to be denied by the political economist. If he deny it, then, and then only, he places himself in the wrong. The à priori method which is laid to his charge, as if his employment of it proved his whole science to be worthless, is, as we shall presently show, the only method by which truth can possibly be attained in any department of the social science. All that is requisite is, that he be on his guard not to ascribe to conclusions which are grounded upon an hypothesis a different kind of certainty from that which really belongs to them. They would be true without qualification, only in a case which is purely imaginary. In proportion as the actual facts recede from the hypothesis, he must allow a corresponding deviation from the strict letter of his conclusion; otherwise it will be true only of things such as he has arbitrarily supposed, not of such things as really exist. That which is true in the abstract, is always true in the concrete with proper allowances. When a certain cause really exists, and if left to itself would infallibly produce a certain effect, that same effect, modified by all the other concurrent causes, will correctly correspond to the result really produced.

The conclusions of geometry are not strictly true of such lines, angles, and figures, as human hands can construct. But no one, therefore, contends that the conclusions of geometry are of no utility, or that it would be better to shut up Euclid's Elements, and content ourselves with "practice" and "experience."

No mathematician ever thought that his definition of a line corresponded to an actual line. As little did any political economist ever imagine that real men had no object of desire but wealth, or none which would not give way to the slightest motive of a pecuniary kind. But they were justified in assuming this, for the purposes of their argument; because they had to do only with those parts of human conduct which have pecuniary advantage for their direct and principal object; and because, as no two individual cases are exactly alike, no general maxims could ever be laid down unless some of the circumstances of the particular case were left out of consideration.

But we go farther than to affirm that the method à priori is a legitimate mode of philosophical investigation in the moral sciences: we contend that it is the only mode. We affirm that the method à posteriori, or that of specific experience, is altogether inefficacious in those sciences, as a means of arriving at any considerable body of valuable truth; though it admits of being usefully applied in aid of the method à priori, and even forms an indispensable supplement to it.

There is a property common to almost all the moral sciences, and by which they are distinguished from many of the physical; this is, that it is seldom in our power to make experiments in them. In chemistry and natural philosophy, we can not only observe what happens under all the combinations of circumstances which nature brings together, but we may also try an indefinite number of new combinations. This we can seldom do in ethical, and scarcely ever in political science. We cannot try forms of government and systems of national policy on a diminutive scale in our laboratories, shaping our experiments as we think they may most conduce to the advancement of knowledge. We therefore study nature under circumstances of great disadvantage in these sciences; being confined to the limited number of experiments which take place (if we may so speak) of their own accord, without any preparation or management of ours; in circumstances, moreover, of great complexity, and never perfectly known to us; and with the far greater part of the processes concealed from our observation.

The consequence of this unavoidable defect in the materials of the induction is, that we can rarely obtain what Bacon has quaintly, but not unaptly, termed an experimentum crucis.

In any science which admits of an unlimited range of arbitrary experiments, an experimentum crucis may always be obtained. Being able to vary all the circumstances, we can always take effectual means of ascertaining which of them are, and which are not, material. Call the effect B, and let the question be whether the cause A in any way contributes to it. We try an experiment in which all the surrounding circumstances are altered, except A alone: if the effect B is nevertheless produced, A is the cause of it. Or, instead of leaving A, and changing the other circumstances, we leave all the other circumstances and change A: if the effect B in that case does not take place, then again A is a necessary condition of its existence. Either of these experiments, if accurately performed, is an experimentum crucis; it converts the presumption we had before of the existence of a connection between A and B into proof, by negativing every other hypothesis which would account for the appearances.

But this can seldom be done in the moral sciences, owing to the immense multitude of the influencing circumstances, and our very scanty means of varying the experiment. Even in operating upon an individual mind, which is the case affording greatest room for experimenting, we cannot often obtain a crucial experiment. The effect, for example, of a particular circumstance in education, upon the formation of character, may be tried in a variety of cases, but we can hardly ever be certain that any two of those cases differ in all their circumstances except the solitary one of which we wish to estimate the influence. In how much greater a degree must this difficulty exist in the affairs of states, where even the number of recorded experiments is so scanty in comparison with the variety and multitude of the circumstances concerned in each. How, for example, can we obtain a crucial experiment on the effect of a restrictive commercial policy upon national wealth? We must find two nations alike in every other respect, or at least possessed, in a degree exactly equal, of everything which conduces to national opulence, and adopting exactly the same policy in all their other affairs, but differing in this only, that one of them adopts a system of commercial restrictions, and the other adopts free trade. This would be a decisive experiment, similar to those which we can almost always obtain in experimental physics. Doubtless this would be the most conclusive evidence of all if we could get it. But let any one consider how infinitely numerous and various are the circumstances which either directly or indirectly do or may influence the amount of the national wealth, and then ask himself what are the probabilities that in the longest revolution of ages two nations will be found, which agree, and can be shown to agree, in all those circumstances except one?

Since, therefore, it is vain to hope that truth can be arrived at, either in Political Economy or in any other department of the social science, while we look at the facts in the concrete, clothed in all the complexity with which nature has surrounded them, and endeavour to elicit a general law by a process of induction from a comparison of details; there remains no other method than the à priori one, or that of "abstract speculation."

Although sufficiently ample grounds are not afforded in the field of politics, for a satisfactory induction by a comparison of the effects, the causes may, in all cases, be made the subject of specific experiment. These causes are, laws of human nature, and external circumstances capable of exciting the human will to action. The desires of man, and the nature of the conduct to which they prompt him, are within the reach of our observation. We can also observe what are the objects which excite those desires. The materials of this knowledge every one can principally collect within himself; with reasonable consideration of the differences, of which experience discloses to him the existence, between himself and other people. Knowing therefore accurately the properties of the substances concerned, we may reason with as much certainty as in the most demonstrative parts of physics from any assumed set of circumstances. This will be mere trifling if the assumed circumstances bear no sort of resemblance to any real ones; but if the assumption is correct as far as it goes, and differs from the truth no otherwise than as a part differs from the whole, then the conclusions which are correctly deduced from the assumption constitute abstract truth; and when completed by adding or subtracting the effect of the non-calculated circumstances, they are true in the concrete, and may be applied to practice.