To make an effort in order to satisfy another’s wants is to render him a ‹service›. If a service is stipulated in return, there is an exchange of ‹services›; and as this is the most ordinary case, Political Economy may be defined ‹the theory of Exchange›. Whatever may be for one of the contracting parties the urgency of the want, or for the other the intensity of the effort, if the exchange is free, the two services exchanged are ‹worth each other›. Value, then, consists in the comparative appreciation of reciprocal ‹services›, and Political Economy again may be defined ‹the theory of Value›. I have just defined Political Economy, and marked out its domain, without mentioning an essential element, ‹gratuitous Utility›. All authors have remarked that we derive a multitude of satisfactions from this source. They denominate these utilities, such as air, water, the light of the sun, etc., ‹natural wealth›, in contradistinction to ‹social wealth›, and having done so, they take no more notice of them; and in fact it would seem that, as they give rise to no effort, to no exchange, to no service, as (being destitute of value) they figure in no inventory of goods, they should not be admitted into the domain of Political Economy. This exclusion would be rational if ‹gratuitous› utility were a fixed invariable quantity, always separated from ‹onerous› utility; but they are constantly mixed up, and in inverse proportions. Man’s constant endeavour is to substitute the one for the other, that is to say, to arrive, by means of natural and gratuitous agents, at the same results as by efforts. He accomplishes by the wind, by gravitation, by heat, by the elasticity of the air, what he accomplished at first only by muscular exertion. Now what happens? Although the effect is equally useful, the effort is less. Less effort implies less service, and less service implies less value. Each step of progress, then, annihilates value; but how? Not by suppressing the useful effect, but by substituting gratuitous for onerous utility, natural for social wealth. In one sense the portion of value thus annihilated is excluded from the domain of Political Economy, just as it is excluded from our inventories. It is no longer exchanged, bought, or sold, and mankind enjoy it without effort and almost without consciousness. It is no longer accounted relative wealth, but is ranked among the gifts of God.