George Grantham Bain Collection; Library of Congress

A basic feature of the criminal justice system is that violent crimes are punished with more prison time than non-violent ones. But the logic behind extremely long sentences is not always clear, reflecting an age-old debate about the purpose of prison.

Whether it’s slashing sentences or reducing the population behind bars, criminal justice reform is now supported by a broad swath of political leaders — left, center and right. But for the most part, the reformers and their rhetoric focus on people accused or convicted of non-violent offenses.

It makes sense to target minor offenses for reforms. But the way violent crimes are kept out of the reform conversation might not be that sensible, as F.T. Green reported here last week.

Here’s a quick primer on what the debate is all about.