Habit Formation and Dynamic Demand Functions

Abstract

Most economists would agree that past consumption patterns are an important determinant of present consumption patterns, and that one ought to distinguish between long-run and short-run demand functions. But although the distinction between long-run and short-run behavior is traditional in the theory of the firm, it is seldom made in the theory of consumer behavior. If we regard demand theory as a theory of how a given amount of money (expenditure, called income) is allocated among goods, then-in a world without consumer durables-there are three reasons why longand shortrun demand functions might differ. (i) The consumer may have contractually fixed commitments which prevent him from adjusting some portion of his consumption (for example, housing) in response to changes in prices or income. When these fixed commitments lapse, he is able to adjust to his long-run equilibrium. (ii) The consumer may be ignorant of consumption possibilities or of his own tastes outside the range of his past consumption experience. In this case his adjustment to a new price-income situation will involve a time-consuming learning process. (iii) Finally, goods may be "habit forming" so that an individual's current preferences depend on his past consumption patterns. In this case a change in prices or income will cause a change-in consumption which will induce a change in tastes, which will cause a further change in consumption. In this paper I formulate a model of consumer behavior based on habit formation, beginning with a specific class of demand functions derived from the "modified Bergson family" of utility functions. The properties of these utility functions and the corresponding demand functions are briefly summarized in Section 1. I then postulate that the parameters