“Capital in the Twenty-First Century,” Thomas Piketty’s new book, has received a great deal of attention. But we shouldn’t neglect another important new book on income inequality, from a much different perspective. Titled “On the Run: Fugitive Life in an American City,” and written by Alice Goffman, a sociologist at the University of Wisconsin, Madison, it offers a fascinating and disturbing portrait of the economic constraints and incentives faced by a large subset of Americans: those who are hiding from the law.

You may think of being on the run as a quandary for only a small group of recalcitrant, hardened criminals. But in her study of one Philadelphia neighborhood, Professor Goffman shows that it is a common way of life for many nonviolent Americans. These people often face charges related to possession or sale of small amounts of drugs, or offenses like hiding relatives from the law. Whatever the negative moral implications of such crimes, they don’t merit having one’s life ruined.

A core point of “On the Run” is that “young men’s compromised legal status transforms the basic institutions of work, friendship and family into a net of entrapment.” For instance, the police round up fugitives by monitoring and contacting their relatives — and that frays family relations. A young man might avoid showing up at the hospital to witness the birth of his child because he knows he could be caught or turned in. Family gatherings become another hazard, so in-person appearances are often surprise visits. People stuck in this kind of limbo are also reluctant to visit hospitals when they need treatment, and a result, the book says, is a “lifestyle of secrecy and evasion,” driven by the unfavorable incentives set in motion by the law.