In a famous letter of 1813, Thomas Jefferson compared the spread
of ideas to the way people light one candle from another: “He
who receives an idea from me, receives instruction himself
without lessening mine; as he who lites his taper at mine,
receives light without darkening me.” The eighteenth-century
ideal of spreading light may seem archaic today, but it can
acquire a twenty-first-century luster if one associates it with
the Internet, which transmits messages at virtually no cost. And
if Internet enthusiasm sounds suspiciously idealistic, one can
extend the chain of associations to a key concept of modern
economics—that of a public good. Public goods such as clean air,
efficient roads, hygienic sewage disposal, and adequate
schooling benefit the entire citizenry, and one citizen’s
benefit does not diminish that of another. Public goods are not
assets in a zero-sum game, but they do carry costs—up-front
costs, usually paid through taxation, at the production end of
the services and facilities that the pub