Prison overcrowding: The magic number IS IT unreasonable for California's state prisons to operate at 137.5% of their capacity? Yes, suggests Jerry Brown; unreasonably restrictive. Last week the governor, under duress, unveiled a plan to reduce the prison population to something closer to what he calls this "somewhat arbitrary" figure. Democrats and Republicans alike agreed with him that this was a terrible idea. But that arbitrary number was insisted on by the Supreme Court two years ago, and the ruling was upheld in April. California leads America in many things. One of them is a mania for locking people up. Tough-talking politicians passed mandatory-sentencing laws like the three-strikes rule, pioneered in California and much imitated elsewhere, which sent third-time offenders to the clink for crimes as minor as shoplifting. Between 1970 and 2007 America's incarceration rate (including county jails) rose roughly fivefold, to 756 per 100,000 people. As spending on incarceration in cash-strapped California soared, other recipients of state largesse, such as universities, saw their budgets slashed. But despite a flurry of prison-building in the 1980s and 1990s, cheered on by officers" unions, California struggled to house the growing aviary of jailbirds. At one point more than twice as many prisoners were stuffed into the state's facilities as they were designed to hold. So in 2009 three federal judges ordered California to cut its prison population from 150,000 to 110,000 within two years. The state appealed, but the Supreme Court was no more receptive to its case. That forced California to embark on one of the great experiments in American incarceration policy: sending criminals convicted of relatively low-level offences to county jails, which have greater discretion over treatment of offenders, rather than to one of the state's 33 prisons. This policy of "realignment," which began in October 2011, has cut the state's prison population by around 25,000. Steven Raphael, a professor of public policy at Berkeley, puts California's incarceration rate (not including county jails) at around 300 per 100,000: well below the national average. Not all California's 58 counties were ready to cope with the new arrivals, says Lenore Anderson, director of Californians for Safety and Justice, a campaign group. Many jails are now over capacity. But in some counties necessity mothered invention. Marin County, north of San Francisco, reduced recidivism rates with "recovery coaches" - former addicts assigned to drug offenders to help them kick the habit. Others freed up space by placing pre-trial detainees who could not afford bail under supervision rather than in detention. For criminologists, realignment was an opportunity to try the sorts of "evidence-based policies" they had been urging on legislators for years. For Mr Brown, it was a way to get the feds off his back. In January, riding high after selling a tax rise to the electorate that returned the state to surplus, Mr Brown unilaterally declared the prison emergency over. Thanks to his policies, he said, California's prison system was now one of the nation's finest, and he would ask the courts to lift their ruling. But California had not met its target, and Mr Brown's breezy speech did not go down well. Last month the three judges firmly denied the governor's request, threatening to hold him in contempt if he maintained his defiance. After at first doing just that, he grimly gave way. The new plan will cut prison numbers further by slowing the return of out-of-state inmates, adding capacity and speeding the release of elderly inmates. It may cost over $200m, says Jeff Beard, the prisons chief. Much of it must be approved by legislators. The plan will not meet the 137.5% target. But Mr Beard says California measures capacity differently from other states, making the number look worse than it is. Mr Brown plans to appeal against the latest ruling, taking it back to the Supreme Court if necessary. He appears to think that, after realignment, its nine justices may look more kindly on his predicament. The row has erupted just as Californians may be turning their back on the lock-"em-up era. In November 69% voted for a slight softening of the state's three-strikes law; polling suggests that a deeper revision could have won approval. There is progress elsewhere, too. States from Kentucky to Ohio have begun experimenting with alternatives to imprisonment, such as expanding the use of "good-time credits," which allow well-behaved inmates to earn their freedom, or "community correction" (expanding parole and probation). The war on drugs, responsible for so many prison sentences, may be easing. By international standards America still imprisons a grotesque number of its citizens. But the number is starting to fall a bit.