Historian Yuval Noah Harari, the author of Sapiens, wrote, “One of history’s few iron laws is that luxuries tend to become necessities and to spawn new obligations.”

As Larry Summers and J. Bradford DeLong would write in August 2001, just a month after the file-sharing service Napster was taken down, ‘the most basic condition for economic efficiency … [is] that price equal marginal cost.’ They went on: ‘with information goods, the social and marginal cost of distribution is close to zero.’ This held true not on

Even if you manage to calculate how many apples equal one pair of shoes, barter is not always possible. After all, a trade requires that each side want what the other has to offer. What happens if the shoemaker doesn’t like apples and, if at the moment in question, what he really wants is a divorce? True, the farmer could look for a lawyer who like