In the previous chapters it was assumed that commodities are produced by means of commodities with (homogeneous) labor as the only “visible” original factor of production. This does not mean, of course, that natural resources were taken to be entirely absent: it means only that they were assumed to be non-scarce. The fish in the sea is not a commodity, it is rather an animal living freely in the water: a “spontaneous rude produce of water,” in the words of Adam Smith. Fish caught and brought to the market however is a commodity. The inputs required to obtain it consist of ships, boats, fuel, fishing-nets, and so on; yet they do not include living fish. But if the catch of today has an effect on tomorrow's catch, or if someone's fishing has an effect on someone else's fishing, then natural resources have explicitly to be taken into account in the analysis. This means that natural resources need to be investigated when they are in short supply, that is, when they are scarce. Whether a particular natural resource will be scarce depends, of course, on the net amounts of the different commodities to be produced, that is, the “requirements for use,” given the quantities of the various natural resources available for capitalist productive purposes and the technological alternatives from which producers can choose. The scarcity of a natural resource is thus not something that should be assumed at the outset: it should rather emerge as a result of the analysis, given the data of the problem under consideration.