Do the courts work?
Ken Clarke says that the debate between himself and Michael Howard about whether prison works is in the past and about the past. It seems to me that the real debate about the future is whether court works.
Michael Howard was the first of a string of home secretaries - Tory and Labour - who effectively said that the courts could not be trusted to mete out justice in a way that would produce public confidence in the criminal justice system.
So he and his successors passed a series of laws to hem judges in. Mr Clarke now says that only the courts - not politicians, the public or, indeed, media headlines - can decide the appropriate sentence in particular cases.
Thus today's sentencing Green Paper for England and Wales will limit the use of so-called "indeterminate sentences", which were created under Tony Blair to ensure that certain prisoners had no fixed release date and had to meet certain conditions before leaving prison.
Currently, I'm told, there are 6,000 such prisoners and a long backlog of case reviews means that they're only being released at a rate of 5% per year. Ken Clarke will propose speeding that up and limiting indeterminate sentences to those serving more than 10 years.
On knife crime, as I reported yesterday, Mr Clarke wants to leave it to judges to decide whether imprisonment is the best response; his party's manifesto had made it clear that judges would be told what to do.
After behind-the-scenes haggling between the Justice Department and No 10, the Green Paper will say that anyone who "commits a crime using a knife" can expect to be sent to prison: a subtle but significant change from the manifesto line that anyone convicted of a knife crime can expect to face a prison sentence.
Not, in other words, those caught in possession of a knife. What's more, the Green Paper will say that juveniles caught carrying a knife should face "serious consequences" - what those will be is less clear.
This debate about whether to trust judges goes beyond the issue of sentencing. It's at the heart of the agonised debate in Whitehall about the future of control orders and Tory angst about the abandonment of their promise to re-write the Human Rights Act.
Ken Clarke and Michael Howard are both lawyers - but one trusts the judges and the other doesn't.