Abstract

In economic theory, commodities are usually classified into different species on the ground of some characteristics which they possess (physical or chemical qualities, spatial or temporal location, the state of nature in which they will be available, etc.); this classification is established once and for all, even before knowing the needs the different commodities can satisfy, or the productive uses they can serve for. On the contrary, in this work the classification into different species will be based on the strictly economic notion of "perfect substitutability" among commodities; therefore, it will be one of the outcomes of the theoretic construction and will depend on households' preferences in an essential way. The very notion of perfect substitutability will also allow the measurement of the commodities belonging to the same species.