The whole point of probation is to keep people out of jail, and the whole point of parole is to get them out of prison. If we can bring them home under supervision, the thinking goes, their return to free society will be safer and more successful than if we just let them loose after their full sentence runs and then hope for the best.

Years of statistics challenge that approach. Probation too often ends up being a gateway into incarceration instead of an alternative. Parole is often a return ticket.

But why?

First, some definitions. Parole refers to a period of time after an inmate is released from state prison early but remains under supervision. It can last weeks, months or even years. Probation is a period of supervision that is ordered in lieu of incarceration altogether.

A comprehensive national study by the Justice Center of the Council of State Governments released last week confirms what has been hinted at for years by anecdotal reports and narrower studies: A large proportion of people “fail” probation or parole and end up back in jail or prison because of conduct that for the rest of us would be perfectly legal, or at least not worthy of incarceration. They might miss a drug rehab appointment, for example, or sit down to lunch with a friend who has a criminal record.

Avoiding people with criminal records is especially difficult in communities unequally affected by drug use and gangs.

These technical violations of probation and parole account for nearly a quarter of all state prison admissions. They turn programs that are supposed to be alternatives to incarceration into a major engine of the jail and prison system. Instead of keeping people out, they keep people in.

That’s counterproductive. Yes, jails and prisons exist to punish people for wrongdoing and to protect public safety. But sending people back for technical and other low-level violations imposes foolish punishment, protects no one and, according to the report, costs $2.8 billion a year.

The justification for locking people up for technical violations is strained. It may be fair to require offenders to follow a set of rules in order to preserve public safety and to demonstrate an ability to live within the law. But it’s foolish and unreasonable to attach so many conditions that they are bound to fail.

Probation and parole conditions are layered on to the many other barriers that states and the federal government erect that prevent successful reentry, like prohibiting former offenders from applying for food or housing assistance, or preventing them from acquiring certain professional licenses. The combination of some conditions and restrictions is especially perverse. How, for example, can a parolee comply with a requirement that he be employed, when at the same time, his conviction makes him ineligible for any job that pays enough to allow him to get an apartment and provide for his family?

When new criminal offenses committed by parolees and probationers are lumped in with technical violations, the percentage of prison admissions due to violating terms of release jumps to 45%.

On first blush, new offenses seem fair game for revoking parole. A crime is more than merely a parole violation. There can be no argument that an armed robber, out on parole, should be sent back to prison for committing another armed robbery.

But it becomes a thornier issue if the parolee’s new crime is something that wouldn’t land most people in jail. It makes sense if the new crime is, say, possession of a gun. That’s legal for most Americans, but paroled bank robbers who put their hands on a weapon deserve a return trip to prison.

But how about possession of a small amount of methamphetamine? That’s a judgment call — and it ought to come before a judge.

And, in fact, it will. In the not-so-good-old days, parole agents had the power to return violators directly to prison without evidentiary hearings or defense lawyers. Court rulings — properly — rejected that process as a violation of even the limited rights of parolees. That’s something often forgotten by critics of California’s criminal justice reforms. It’s not Proposition 47 or Assembly Bill 109 that restricted the once-unfettered power of parole agents. It’s the Constitution.

Reforms have helped drive down the proportion of California prison and jail inmates who are there because of technical probation and parole violations. That’s good, but it’s still too high. A careful review of laws and regulations that impose technical violations can help distinguish among those that should be kept on the books, those that should apply only in the narrowest circumstances and those that ought to be thrown out altogether.