Marx's mistake has been that he has inadvertently attributed a _greater value_ to the fixed capital, which after the technical improvement is worked by the same labourers as before. Certainly anyone who looks at a society in two successive stages of technical development, will find in the second stage a greater number of machines and of tools of every kind. _This is a question of statistics, not of economics._ Capital (and Marx appears to have neglected this point for the moment) is not estimated by its physical extension, but by its economic value. And economically that capital (supposing all the other conditions remain constant) _must be worth less_; otherwise no technical improvement would have taken place. An external circumstance which might serve to explain Marx's error is the fact that the third book of _Das Kapital_ is a posthumous work, some parts of which are hardly sketched out, and amongst these that of the _law of the rate of profits_, which, moreover, does not relate to the _establishment of principles_, but, being a consequence and an application or these, was perhaps not worked out to the same extent as the fundamental or central part of the theory.[91] It is probable that the author, if he could have gone over his rough draft again, would have materially modified it or entirely discarded it. But perhaps some internal reason could also be found for this strange mistake, in that Marx always misused the comparative method without disclosing any distinct knowledge of his procedure. And it might be that, as already in his earlier investigations, he perpetually transferred labour-value from a hypothetical society to the actual capitalist society, so in this new problem he has been led to estimate the worth of the technical capital in a more advanced society at the rate of value of that in a less advanced society. In this impossible attempt his method has here broken in his hands. As we have disputed the actual basis of the Marxian law, it seems indeed superfluous to follow out its further developments, which are advanced in a form worked out with but little care. It is enough to remark that in these developments, as in general, throughout _Das Kapital_, there is a continuous medley of theoretical deductions and historical descriptions, of logical and of material connections. The defect, however, becomes in this instance an advantage, because many of the observations made by Marx, understood as historical descriptions of what usually happens in modern society, will be found to be true and can be saved from the shipwreck, as regards the theory of the law, with which by chance they are feebly connected. And it would even be possible to make such an investigation in respect to that very portion which we have disputed, _i.e._ to enquire what _facts_, actually observed by him, could have impelled Marx to construct his law, _i.e._ to give of these facts an explanation which is theoretically unjustifiable.