Thus, in no other species are the faculties so susceptible of vast development as in man. It is his alone to compare and to judge, to reason and to speak, to foresee, to sacrifice the present to the future. He alone can transmit, from generation to generation, his works, his thoughts, the treasures of his experience. He alone is capable of a perfectibility which is indefinite, which forms a chain the countless links of which would seem to stretch beyond the limits of the present world. Let me here set down an observation which belongs properly to Political Economy. However extended may be the domain of our faculties, they do not reach the length of ‹creating› anything. Man cannot, in truth, augment or diminish the number of existing particles of matter. His action is limited to subjecting the substances which he finds around him to modifications and combinations which fit them for his use.[25] To modify substances, so as to increase their utility in relation to us, is to ‹produce›, or rather it is one mode of producing. From this I conclude that value (as we shall afterwards more fully explain) does not reside in these substances themselves, but in the effort which intervenes in order to modify them, and which exchange brings into comparison with other analogous efforts. This is the reason why value is simply the appreciation of services exchanged, whether a material commodity does or does not intervene. As regards the notion of value, it is a matter of perfect indifference whether I render to another a direct service, as, for example, in performing for him a surgical operation, or an indirect service, in preparing for him a curative substance. In this last case the ‹utility› is in the substance, but the ‹value› is in the service, in the effort, intellectual and muscular, made by one man for the benefit of another. It is by a pure metonymy that we attribute value to the material substance itself, and here, as on many other occasions, metaphor leads science astray. I return to the subject of man’s organization. If we adhere to the preceding notions, he differs from other animals only in the greater extent of his wants, and the superiority of his powers. All, in fact, are subject to the one and provided with the other. A bird undertakes long journeys in search of the temperature which suits it best—the beaver crosses the river on a bridge of [p101] his own construction—the hawk pursues his prey openly—the cat watches for it with patience—the spider prepares a snare—all labour in order to live and multiply.