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The concept of Utility

24 April, 2015 - 11:52

Learning Objectives

  • Define what economists mean by utility.
  • Distinguish between the concepts of total utility and marginal utility.
  • State the law of diminishing marginal utility and illustrate it graphically.
  • State, explain, and illustrate algebraically the utility-maximizing condition.

Why do you buy the goods and services you do? It must be because they provide you with satisfaction you feel better off because you have purchased them. Economists call this satisfaction utility.

The concept of utility is an elusive one. A person who consumes a good such as peaches gains utilityfrom eating the peaches. But we cannot measure this utility the same way we can measure a peach’s weight or calorie content. There is no scale we can use to determine the quantity of utility a peach generates.

Francis Edgeworth, one of the most important contributors to the theory of consumer behavior,imagined a device he called a hedonimeter (after hedonism, the pursuit of pleasure):

Let there be granted to the science of pleasure what is granted to the science of energy; toimagine an ideally perfect instrument, a psychophysical machine, continually registering the height of pleasure experienced by an individual…. From moment to moment the hedonimetervaries; the delicate index now flickering with the flutter of passions, now steadied by intellectual activity, now sunk whole hours in the neighborhood of zero, or momentarily springing up towards infinity.

Source: Francis Y. Edgeworth, Mathematical Psychics: An Essay on the Application of Mathematics to the Moral Sciences (New York: Augustus M. Kelley, 1967), p. 101. First Published 1881.

Perhaps some day a hedonimeter will be invented. The utility it measures will not be a characteristicof particular goods, but rather of each consumer’s reactions to those goods. The utility of a peachexists not in the peach itself, but in the preferences of the individual consuming the peach. One consumer may wax ecstatic about a peach; another may say it tastes OK.

When we speak of maximizing utility, then, we are speaking of the maximization of something wecannot measure. We assume, however, that each consumer acts as if he or she can measure utility and arranges consumption so that the utility gained is as high as possible.