All this week Melvyn Bragg and guests are discussing ideas of Justice. Today lawyer Harry Potter uses the ideas of the philosopher Kant to ask whether deterrent prison sentences are just. He takes us back to the 1700s, when hundreds of petty offences carried the death penalty. And Gordon Finlayson from the University of Sussex explains how Kant's idea that you should never treat people as a means to an end would put him at odds with our justice system today, where people can receive heavy sentences in order to put others off committing the same crime. To see whether Kant's ideas and our justice system can be reconciled, Harry visits Lord Judge who was Lord Chief Justice at the time of the London riots of 2011, when deterrent sentences were handed down. He explains how sentences are determined. Producer: Melvin Rickarby.