The nature in terms of which all knowledge of phenomena--for the present purpose economic phenomena--is to be finally synthesised is, therefore, substantially of a quasi-spiritual or animistic character. The laws of nature are in the last resort teleological: they are of the nature of a propensity. The substantial fact in all the sequences of nature is the end to which the sequence naturally tends, not the brute fact of mechanical compulsion or causally effective forces. Economic theory is accordingly the theory (1) of how the efficient causes of the _ordre naturel_ work in an orderly unfolding sequence, guided by the underlying natural laws--the propensity immanent in nature to establish the highest well-being of mankind, and (2) of the conditions imposed upon human conduct by these natural laws in order to reach the ordained goal of supreme human welfare. The conditions so imposed on human conduct are as definitive as the laws and the order by force of which they are imposed; and the theoretical conclusions reached, when these laws and this order are known, are therefore expressions of absolute economic truth. Such conclusions are an expression of reality, but not necessarily of fact.
Now, the objective end of this propensity that determines the course of nature is human well-being. But economic speculation has to do with the workings of nature only so far as regards the _ordre physique_. And the laws of nature in the _ordre physique_, working through mechanical sequence, can only work out the physical well-being of man, not necessarily the spiritual. This propensity to the physical well-being of man is therefore the law of nature to which economic science must bring its generalisations, and this law of physical beneficence is the substantial ground of economic truth. Wanting this, all our speculations are vain; but having its authentication they are definitive. The great, typical function, to which all the other functioning of nature is incidental if not subsidiary, is accordingly that of the alimentation, nutrition of mankind. In so far, and only in so far as the physical processes contribute to human sustenance and fullness of life, can they, therefore, further the great work of nature. Whatever processes contribute to human sustenance by adding to the material available for human assimilation and nutrition, by increasing the substance disposable for human comfort, therefore count towards the substantial end. All other processes, however serviceable in other than this physiological respect, lack the substance of economic reality. Accordingly, human industry is productive, economically speaking, if it heightens the effectiveness of the natural processes out of which the material of human sustenance emerges; otherwise not. The test of productivity, of economic reality in material facts, is the increase of nutritive material. Whatever employment of time or effort does not afford an increase of such material is unproductive, however profitable it may be to the person employed, and however useful or indispensable it may be to the community. The type of such productive industry is the husbandman's employment, which yields a substantial (nutritive) gain. The artisan's work may be useful to the community and profitable to himself, but its economic effect does not extend beyond an alteration of the form in which the material afforded by nature already lies at hand. It is formally productive only, not really productive. It bears no part in the creative or generative work of nature; and therefore it lacks the character of economic substantiality. It does not enhance nature's output of vital force. The artisan's labors, therefore, yield no net product, whereas the husbandman's labors do.