Essays on some unsettled Questions of Political Economy

by John Stuart Mill

But, further, the recognised boundaries which separate the field of Political Economy from that of physical science, by no means correspond with the distinction between the truths which concern all kinds of wealth and those which relate only to some kinds. The three laws of motion, and the law of gravitation, are common, as far as human observation has yet extended, to all matter; and these, therefore, as being among the laws of the production of all wealth, should form part of Political Economy. There are hardly any of the processes of industry which do not partly depend upon the properties of the lever; but it would be a strange classification which included those properties among the truths of Political Economy. Again, the latter science has many inquiries altogether as special, and relating as exclusively to particular sorts of material objects, as any of the branches of physical science. The investigation of some of the circumstances which regulate the price of corn, has as little to do with the laws common to the production of all wealth, as any part of the knowledge of the agriculturist. The inquiry into the rent of mines or fisheries, or into the value of the precious metals, elicits truths which have immediate reference to the production solely of a peculiar kind of wealth; yet these are admitted to be correctly placed in the science of Political Economy.

The real distinction between Political Economy and physical science must be sought in something deeper than the nature of the subject-matter; which, indeed, is for the most part common to both. Political Economy, and the scientific grounds of all the useful arts, have in truth one and the same subject-matter; namely, the objects which conduce to man's convenience and enjoyment: but they are, nevertheless, perfectly distinct branches of knowledge.

3. If we contemplate the whole field of human knowledge, attained or attainable, we find that it separates itself obviously, and as it were spontaneously, into two divisions, which stand so strikingly in opposition and contradistinction to one another, that in all classifications of our knowledge they have been kept apart. These are, physical science, and moral or psychological science. The difference between these two departments of our knowledge does not reside in the subject-matter with which they are conversant: for although, of the simplest and most elementary parts of each, it may be said, with an approach to truth, that they are concerned with different subject-matters—namely, the one with the human mind, the other with all things whatever except the mind; this distinction does not hold between the higher regions of the two. Take the science of politics, for instance, or that of law: who will say that these are physical sciences? and yet is it not obvious that they are conversant fully as much with matter as with mind? Take, again, the theory of music, of painting, of any other of the fine arts, and who will venture to pronounce that the facts they are conversant with belong either wholly to the class of matter, or wholly to that of mind?

The following seems to be the rationale of the distinction between physical and moral science.

In all the intercourse of man with nature, whether we consider him as acting upon it, or as receiving impressions from it, the effect or phenomenon depends upon causes of two kinds: the properties of the object acting, and those of the object acted upon. Everything which can possibly happen in which man and external things, are jointly concerned, results from the joint operation of a law or laws of matter, and a law or laws of the human mind. Thus the production of corn by human labour is the result of a law of mind, and many laws of matter. The laws of matter are those properties of the soil and of vegetable life which cause the seed to germinate in the ground, and those properties of the human body which render food necessary to its support. The law of mind is, that man desires to possess subsistence, and consequently wills the necessary means of procuring it.

Laws of mind and laws of matter are so dissimilar in their nature, that it would be contrary to all principles of rational arrangement to mix them up as part of the same study. In all scientific methods, therefore, they are placed apart. Any compound effect or phenomenon which depends both on the properties of matter and on those of mind, may thus become the subject of two completely distinct sciences, or branches of science; one, treating of the phenomenon in so far as it depends upon the laws of matter only; the other treating of it in so far as it depends upon the laws of mind.

The physical sciences are those which treat of the laws of matter, and of all complex phenomena in so far as dependent upon the laws of matter. The mental or moral sciences are those which treat of the laws of mind, and of all complex phenomena in so far as dependent upon the laws of mind.

Most of the moral sciences presuppose physical science; but few of the physical sciences presuppose moral science. The reason is obvious. There are many phenomena (an earthquake, for example, or the motions of the planets) which depend upon the laws of matter exclusively; and have nothing whatever to do with the laws of mind. Many, therefore, of the physical sciences may be treated of without any reference to mind, and as if the mind existed as a recipient of knowledge only, not as a cause producing effects. But there are no phenomena which depend exclusively upon the laws of mind; even the phenomena of the mind itself being partially dependent upon the physiological laws of the body. All the mental sciences, therefore, not excepting the pure science of mind, must take account of a great variety of physical truths; and (as physical science is commonly and very properly studied first) may be said to presuppose them, taking up the complex phenomena where physical science leaves them.

Now this, it will be found, is a precise statement of the relation in which Political Economy stands to the various sciences which are tributary to the arts of production.

The laws of the production of the objects which constitute wealth, are the subject-matter both of Political Economy and of almost all the physical sciences. Such, however, of those laws as are purely laws of matter, belong to physical science, and to that exclusively. Such of them as are laws of the human mind, and no others, belong to Political Economy, which finally sums up the result of both combined.