The Discreet Charm of Substitutability. On Rudolf Auspitz and Richard Lieben's uses of Substitutes and Complements in Consumption.

Rudolf Auspitz and Richard Lieben's Untersuchungen über die Theorie des Preises (1889) are an important contribution to the rise of mathematical economics. A distinguishing feature of their work is to consider utility of one commodity as a function of the quantities of all commodities, and to provide the first formal definition of competing and completing goods. On many occasions, they draw attention to the fact that consumers can choose among substitutes. The aim of this paper is to provide a rational explanation of the uses of substitutes and complements in their work. It is argued that the hypothesis about substitutes is very useful to them in establishing a sophisticated analysis of consumer rent, deprived of some ethical restrictions.