_Second_, that men, as not only imperfect in nature but erring in judgment, have made an easy extension of the term “human life” to cover “human desire,” and count things valuable because they satisfy some want or other. The economic “want” is not necessarily a rational or a healthy want—and political economy, as primarily analytic, must not be censured for the statement, nor condemned as if it approved of the fact—but simply a want, and the things which satisfy such wants we call “goods.” The _desirable_ is interpreted in economics by the _desired_. _Third_, that the element of scarcity somehow plays a large part in many, and seems to have a share in all, estimates of value. Were it not for this element of scarcity one might conclude that the “valuable” and the “useful” were synonymous terms. Few writers have been careful to keep the two conceptions sufficiently separate, and the distinction which we have now to draw, while contained in Ricardo, was not scientifically formulated till the appearance of Menger’s _Grundsätze_ in 1871. The economically Useful is that which is capable of satisfying the want of man—always meaning by “want” no more than “desire.”[5] Corresponding with this conception, economically, is that of the “Good.”[6] To constitute a good, four things, according to Menger, are required: (1) a human want, (2) certain properties in an object which make it capable of satisfying a human want, (3) the knowledge of this capability, (4) power to dispose of this object in the satisfaction of want. In these two conceptions, the Useful and the Good, there is no reference to scarcity. [5] “Anything which an individual is found to desire and to labour for must be assumed to possess for him utility. In the science of Economics we treat men, not as they ought to be, but as they are.”—Jevons, _Theory_, 2d Edition, p. 41. [6] It is one of the difficulties of our economic vocabulary that, where we wish to express the singular of “goods,” we have to use “commodity” or some such word. In my translations, I have made no scruple of rendering the honest German _Gut_ by its literal equivalent, and it is in this sense that the word is used above and throughout this book. It will be noted in what follows that there is a difference between simple goods and “economic goods.”