The doctrine of the social-economic function of the undertaker may for the present purpose be illustrated by a supposititious parallel from Physics. It is an easy generalisation, which will scarcely be questioned, that, in practice, pendulums commonly vibrate in a plane approximately parallel with the nearest wall of the clock-case in which they are placed. The normality of this parallelism is fortified by the further observation that the vibrations are also commonly in a plane parallel with the nearest wall of the room; and when it is further called to mind that the balance which serves the purpose of a pendulum in watches similarly vibrates in a plane parallel with the walls of its case, the absolute normality of the whole arrangement is placed beyond question. It is true, the parallelism is not claimed to be related to the working of the pendulum, except as a matter of fortuitous convenience; but it should be manifest from the generality of the occurrence that in the normal case, in the absence of disturbing causes, and in the long run, all pendulums will "naturally" tend to swing in a plane faultlessly parallel with the nearest wall. The use which has been made of the "organic concept," in economics and in social science at large, is fairly comparable with this supposititious argument concerning the pendulum. [9] Since the ground of payment of wages is the vendibility of the product, and since the ground of a difference in wages is the different vendibility of the product acquired through the purchase of the labor for which the wages are paid, it follows that wherever the difference in vendibility rests on a difference in the magnitude of the product alone, there wages should be somewhat in proportion to the magnitude of the product. [10] All wealth so used is capital, but it does not follow that all pecuniary capital is social wealth. [11] In current theory the term capital is used in these two senses; while in business usage it is employed pretty consistently in the former sense alone. The current ambiguity in the term capital has often been adverted to by economists, and there may be need of a revision of the terminology at this point; but this paper is not concerned with that question. [12] Professor Fetter, in a recent paper (_Quarterly Journal of Economics_, November, 1900) is, perhaps, the writer who has gone the farthest in this direction in the definition of the capital concept. Professor Fetter wishes to confine the term capital to pecuniary capital, or rather to such pecuniary capital as is based on the ownership of material goods. The wisdom of such a terminological expedient is, of course, not in question here. ON THE NATURE OF CAPITAL[1] I. THE PRODUCTIVITY OF CAPITAL GOODS