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the equal dependence, namely, of the science of Political Economy on the laws of the physical world and on those of the human mind—if we consider that a change in the character of the former laws will equally affect its conclusions with a change in that of the latter. The physical qualities of the soil, e. g. under the present constitution of nature are such, that, after a certain quantum of cultivation has been applied to a limited area, a further application is not attended with a proportionate return. The proof of this is, that, instead of confining cultivation to the best soils, and forcing them to yield the whole amount of food that may be required, it is found profitable to resort to soils of inferior quality.*
* This doctrine has been denied, and some curious arguments have been advanced in refutation of it. The topic most insisted on by those who controvert it is the superior productiveness of agricultural industry in the United Kingdom at present, as compared with that which prevailed in former periods, notwithstanding the greater amount of capital now employed in agriculture. This argument would be good for something if all the other conditions of the problem were the same; but it is certain that they are not the same, and that they differ precisely in the point that is of importance—the superior skill with which capital and industry are at present applied. No economist, that I am aware of, has ever said that a small and unskilful application of capital to land would necessarily be attended with greater proportional returns than a larger outlay more skilfully applied ; and it is to this assertion only that the argument in question applies.
But it is important to remark that the attempt to meet the doctrine in question by statistical data implies a total misconception, both of the fact which is asserted, and of the kind of proof which an economic doctrine requires. The doctrine contains, not an historic generalization to be tested by documentary evidence, but a statement as to an existing physical fact, which, if seriously questioned, can only be conclusively determined by actual experiment upon the existing soil. If
This physical fact, as every Political Economist knows, and as shall be explained on a future occasion, leads, through the play of human desires in the pursuit of wealth, to the phenomenon of rent, to the fall of profits as communities advance, and to a retardation
any one denies the fact, it is open to him to refute it by making the experiment. Let him show that he can obtain from a limited area of soil any required quantity of produce by simply increasing the outlay —that is to say, that, by quadrupling or decupling the outlay, he can obtain a quadruple or decuple return. If it be asked why those who maintain the affirmative of the doctrine do not establish their view by actual experiment, the answer is, that the experiment is performed for them by every practical farmer ; and that the fact of the diminishing productiveness of the soil, is proved by their conduct in preferring to resort to inferior soils, rather than force unprofitably soils of better quality.
Mr. Carey, the American economist, has endeavoured to meet this reasoning by urging, that the conduct of farmers in resorting to inferior soils after the better qualities have been all taken into cultivation no more constitutes a proof that industry on the superior soils has become less productive, than the conduct of a cotton spinner in building a second factory, when his first is full, is a proof that manufacturing industry tends to become less productive, as manufacturing capital and labour increase. This is, in other words, to say, that the reason farmers do not increase their outlay on the soils of superior quality is, not because it would be unprofitable to do so, but for the same reason which limits the amount of capital and the number of hands employed in a cotton mill, namely, that, the necessary conditions of space being taken into account, it would be impossible to do so. No one who holds the received theory of rent will hesitate to stake the doctrine upon this issue. When any sane farmer in the United Kingdom, or in any other quarter of the civilized world, will give the same answer to the question—"why he does not manure more highly, or drain more deeply, or plough more frequently, a given field”, which Mr. Carey gives-viz. “ want of room”, the disciples of Ricardo will be prepared to abandon their master ; but, till this specimen of bucolic exegesis is produced, they will probably retain their present views.
in the advance of population. If the fact were otherwise, if the physical properties of the soil were such as to admit of an indefinite increase of produce in undiminished proportion to the outlay by simply increasing the outlay—if e. g., it were found that by doubling the quantity of manure upon a given acre and by ploughing it twice as often, a farmer could obtain a double produce, and by quadrupling them, a quadruple produce, and so on ad infinitum; if this were so, the science of Political Economy, as it at present exists, would be as completely revolutionized as if human nature itself were altered—as if benevolence, for example, were so strengthened at the expense of self-love, that human beings should refuse to avail themselves, at the expense of their neighbours, of those special advantages with which nature or fortune may happen to invest them ; under such a change in the physical qualities of the soil rent would disappear, profits would have no tendency permanently to fall, and population in the oldest countries might advance as rapidly as in the newest colonies.
I am therefore disposed to regard Political Economy as belonging neither to the department of physical nor to that of mental inquiry, but as occupying an intermediate position, and as referable to the class of studies which includes historical, political, and social investigations. The class appears to me to be a class sui generis, having for its subject-matter the complex phenomena presented by the concurrence of physical, physiological, and mental laws, and for its function the tracing of such phenomena to their physical, physiological, and mental causes.
Thus, to take an example from Political Economy, rent is a complex phenomenon, arising (as has been already intimated) from the play of human interests when brought into contact with the actual physical conditions of the soil, in relation to the physiological character of vegetable productions. If these physical conditions were different, if capital and labour could be applied to a limited portion of the soil indefinitely with undiminished return, a small portion only of the best land in the country would be cultivated, and no farmer would consent to pay rent : on the other hand, if the principle of self-interest were absent, no landlord would exact it. Both conditions are indispensable, and equally indispensable, to the existence of rent : they are the premises from which the theory is deduced. It is for the political economist to prove, first, that the premises are true in fact ; and, secondly, that they account for the phenomenon ; but when this is done, his business is ended. He does not | attempt to explain the physical laws on which the qualities of the soil depend ; and no more does he undertake to analyze the nature of those feelings of self-interest in the minds of the landlord and tenant which regulate the terms of the bargain. He regards them both as facts, not to be analyzed and explained, but to be ascertained and taken account of; not as the subject-matter, but as the basis of his reasonings. If further information be desired, recourse must be had to other sciences : the physical fact he hands over to the chemist or the physiologist; the mental to the psychological or the ethical scholar.*
The position of Political Economy, in this respect, appears to me to be entirely analogous to that of Geology in relation to the sciences of Mechanics, Chemistry, and Physiology. The complex phenomena presented by the constitution of the earth's crust form the subject-matter of the science of the geologist; they are the complex result of mechanical, chemical, and physiological laws, and the business of the geologist is to trace them to these causes ; but, having done this, his labours as a geologist are at an end : the further investigation of the problem belongs not to Geology, but to Mechanics, Chemistry, and Physiology.
The premises, or ultimate facts, of Political Economy being thus drawn alike from the world of matter and from that of mind, it remains that I should indicate the character of those facts, physical and mental, which are to be regarded as belonging to the science; in other words, that I should show in what manner the facts which are pertinent to economic investigations are to be distinguished from those which are not. The answer to this question must in general be determined by considering what the science proposes to accomplish. This, as you are aware, is the discovery of the laws of the production and distribution of wealth. The facts, therefore, which constitute
* Appendix B.