Now in all questions connected with progressive social action the effects which have to be considered are not general effects, such as running at some indeterminate speed, each of which effects is considered as being single of its kind, and which, in consequence, cannot be compared with anything, but effects each kind of which exhibits many comparable varieties, such as the running of several men whose respective speeds are different. The whole error of Mill’s argument depends on his failure to perceive this. He describes the result of man’s labour applied to land—a result which we have for convenience’ sake expressed in terms of loaves as “_the_ effect.” He says “_nature and labour are equally necessary for producing the effect at all_,” as though the same amount of land and {202} labour must always result in the production of the same number of loaves. To conceive and speak of the matter in this way is to ignore entirely all the phenomena of progress—all the phenomena which differentiate civilisation from savagery, and which it is the special function of economics and of sociology to explain. Rent, for example, the theory of which Mill states with extreme lucidity, and insists upon with the utmost emphasis, arises from the fact that one man and one acre of land, instead of producing something that can be described generally as “_the_ effect,” produce in different cases effects that are widely different—ten loaves when the acre is bad, twenty loaves when the acre is good: and, in a similar way, when the acres are of the same quality, twenty loaves will be produced by an acre if it is cultivated by the methods of civilisation, and only ten by an acre if it is cultivated by the methods of a savage. Now, just as agricultural rent arises from different qualities in the soil, so does agricultural progress arise from differences in the powers of the men. It is measured by, and it consists of, not “_the_ effect,” but a series of effects, similar indeed in kind, but continually increasing in degree; and it is their differences in degree, not their similarity in kind, that form for the economist the particular subject to be considered.