Political Economy, then, may be defined as follows; and the definition seems to be complete:—
"The science which traces the laws of such of the phenomena of society as arise from the combined operations of mankind for the production of wealth, in so far as those phenomena are not modified by the pursuit of any other object."
But while this is a correct definition of Political Economy as a portion of the field of science, the didactic writer on the subject will naturally combine in his exposition, with the truths of the pure science, as many of the practical modifications as will, in his estimation, be most conducive to the usefulness of his work.
The above attempt to frame a stricter definition of the science than what are commonly received as such, may be thought to be of little use; or, at best, to be chiefly useful in a general survey and classification of the sciences, rather than as conducing to the more successful pursuit of the particular science in question. We think otherwise, and for this reason; that, with the consideration of the definition of a science, is inseparably connected that of the philosophic method of the science; the nature of the process by which its investigations are to be carried on, its truths to be arrived at.
Now, in whatever science there are systematic differences of opinion—which is as much as to say, in all the moral or mental sciences, and in Political Economy among the rest; in whatever science there exist, among those who have attended to the subject, what are commonly called differences of principle, as distinguished from differences of matter-of-fact or detail,—the cause will be found to be, a difference in their conceptions of the philosophic method of the science. The parties who differ are guided, either knowingly or unconsciously, by different views concerning the nature of the evidence appropriate to the subject. They differ not solely in what they believe themselves to see, but in the quarter whence they obtained the light by which they think they see it.
The most universal of the forms in which this difference of method is accustomed to present itself, is the ancient feud between what is called theory, and what is called practice or experience. There are, on social and political questions, two kinds of reasoners: there is one portion who term themselves practical men, and call the others theorists; a title which the latter do not reject, though they by no means recognise it as peculiar to them. The distinction between the two is a very broad one, though it is one of which the language employed is a most incorrect exponent. It has been again and again demonstrated, that those who are accused of despising facts and disregarding experience build and profess to build wholly upon facts and experience; while those who disavow theory cannot make one step without theorizing. But, although both classes of inquirers do nothing but theorize, and both of them consult no other guide than experience, there is this difference between them, and a most important difference it is: that those who are called practical men require specific experience, and argue wholly upwards from particular facts to a general conclusion; while those who are called theorists aim at embracing a wider field of experience, and, having argued upwards from particular facts to a general principle including a much wider range than that of the question under discussion, then argue downwards from that general principle to a variety of specific conclusions.
Suppose, for example, that the question were, whether absolute kings were likely to employ the powers of government for the welfare or for the oppression of their subjects. The practicals would endeavour to determine this question by a direct induction from the conduct of particular despotic monarchs, as testified by history. The theorists would refer the question to be decided by the test not solely of our experience of kings, but of our experience of men. They would contend that an observation of the tendencies which human nature has manifested in the variety of situations in which human beings have been placed, and especially observation of what passes in our own minds, warrants us in inferring that a human being in the situation of a despotic king will make a bad use of power; and that this conclusion would lose nothing of its certainty even if absolute kings had never existed, or if history furnished us with no information of the manner in which they had conducted themselves.
The first of these methods is a method of induction, merely; the last a mixed method of induction and ratiocination. The first may be called the method à posteriori; the latter, the method à priori. We are aware that this last expression is sometimes used to characterize a supposed mode of philosophizing, which does not profess to be founded upon experience at all. But we are not acquainted with any mode of philosophizing, on political subjects at least, to which such a description is fairly applicable. By the method à posteriori we mean that which requires, as the basis of its conclusions, not experience merely, but specific experience. By the method à priori we mean (what has commonly been meant) reasoning from an assumed hypothesis; which is not a practice confined to mathematics, but is of the essence of all science which admits of general reasoning at all. To verify the hypothesis itself à posteriori, that is, to examine whether the facts of any actual case are in accordance with it, is no part of the business of science at all, but of the application of science.
In the definition which we have attempted to frame of the science of Political Economy, we have characterized it as essentially an abstract science, and its method as the method à priori. Such is undoubtedly its character as it has been understood and taught by all its most distinguished teachers. It reasons, and, as we contend, must necessarily reason, from assumptions, not from facts. It is built upon hypotheses, strictly analogous to those which, under the name of definitions, are the foundation of the other abstract sciences. Geometry presupposes an arbitrary definition of a line, "that which has length but not breadth." Just in the same manner does Political Economy presuppose an arbitrary definition of man, as a being who invariably does that by which he may obtain the greatest amount of necessaries, conveniences, and luxuries, with the smallest quantity of labour and physical self-denial with which they can be obtained in the existing state of knowledge. It is true that this definition of man is not formally prefixed to any work on Political Economy, as the definition of a line is prefixed to Euclid's Elements; and in proportion as by being so prefixed it would be less in danger of being forgotten, we may see ground for regret that this is not done. It is proper that what is assumed in every particular case, should once for all be brought before the mind in its full extent, by being somewhere formally stated as a general maxim. Now, no one who is conversant with systematic treatises on Political Economy will question, that whenever a political economist has shown that, by acting in a particular manner, a labourer may obviously obtain higher wages, a capitalist larger profits, or a landlord higher rent, he concludes, as a matter of course, that they will certainly act in that manner. Political Economy, therefore, reasons from assumed premises—from premises which might be totally without foundation in fact, and which are not pretended to be universally in accordance with it. The conclusions of Political Economy, consequently, like those of geometry, are only true, as the common phrase is, in the abstract; that is, they are only true under certain suppositions, in which none but general causes—causes common to the whole class of cases under consideration—are taken into the account.