[Excerpt] Unavailability's enhancement of value has not escaped the attention of psychologists. In 1968, Timothy Brock presented a theory that is reminiscent of Smith's observations. According to commodity theory, anything that is potentially possessable and useful to its possessors will be valued to the extent that its availability is limited by scarcity, costliness, restrictions, and/or delays. Empirical tests of this theory have found strong support for its predictions (see Lynn, 1991, for a review), so modem psychological theory and research appears to agree with conventional wisdom on this issue. Unavailability does sometimes increase the desirability of things, but why? Economists, philosophers, and sociologists have tended to attribute the appeal of unavailable commodities to human vanity. According to these theorists, people desire unavailable (i.e., scarce and expensive) things because the ostentatious display of such possessions is a source of status (cf, Rae, 1905; Simmel, 1957; Smith, 1937; Veblen, 1965). Although it is undoubtedly true that the desire for status and social position underlies the demand for many scarce and expensive things, this is at best a partial explanation for unavailability's enhancement of desirability.